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This work investigated the strength degradation mechanisms of seawater ordinary Portland cement (OPC) pastes. Two types of specimens were prepared ((i) OSD sample (i.e. OPC was mixed with seawater, and then cured in deionized (DI) water) and (ii) ODD sample (i.e. OPC was mixed with DI water, and then cured in DI water, as the reference system)). The use of seawater in preparing OPC pastes effectively increased the hydration rate and early-age mechanical strength, but lowered the mechanical strength at the later age. The higher hydration degree and larger amounts of carbonates with a smaller crystal size enabled the seawater OPC pastes to exhibit a higher early-age mechanical strength, increasing by 13.0%–17.0% compared with the DI water OPC pastes. While the formation of Friedel’s salt and the formation of calcium-silicate-hydrate (C-S-H) gel with a lower polymerization degree and mean molecular chain length resulted in the deterioration of the pore structure and negatively affected the later-age strength development of the seawater OPC paste, decreasing by 5.8%–11.9% compared with the DI water OPC pastes.

This study investigated the compressive strength, drying shrinkage and alkali-silica reaction (ASR) expansion of alkali-activated mortars using sand or glass cullet (GC) as aggregates and using glass powder (GP) to partially replace ground granulated furnace slag (GGBS) as the precursor. For mortars using GC as the aggregate, the replacement of GGBS by GP decreased the compressive strength. The mortars using sand as aggregate showed severe drying shrinkage and the replacement of sand by GC could significantly decrease the drying shrinkage. The addition of calcium aluminium cement (CAC) could further suppress the drying shrinkage. The alkali-activated GGBS mortars using GC as the aggregate showed large expansion after alkaline immersion. When using GP to partially replace GGBS, the expansion was significantly decreased. The replacement of 15% GGBS by CAC could further decrease the expansion. The optimal alkali-activated cement (AAC) mixture proportion developed in this study was the mortars incorporating 15% of CAC, 10% of GGBS and 75% of GP as the compressive strength, expansion and drying shrinkage of this mixture could meet the stipulated mechanical and durability requirements for partition wall applications.

This paper presents an innovative way of enhancing the residual strength and the dimensional stability after elevated temperature exposures for Alkali Activated Cement (AAC) mortar prepared with recycled glass materials as the principle precursor and fine aggregate. The reference AAC mixture was prepared with Glass Powder (GP) solely as the precursor material. A 28-day compressive strength of slightly over 10 MPa was attained but the samples experienced severe dimensional instability (expansion) after 2 h of exposure to 800 °C. To address this problem, 10% to 25% calcium aluminate cement (CAC) was used to replace the GP and the expansion was effectively controlled when the amount of CAC reached 15%. Also, significant strength increment was attained after the elevated temperature resistance test. The severe expansion of the reference mortar was attributed to the density reduction and volume expansion of the recycled glass materials at the elevated temperature and an extremely porous structure (porosity of over 50%) was resulted after the test. Meanwhile, for the CAC incorporated mixtures, the dehydration of sodium aluminum silicate hydrate at temperature ranging from 250–270 °C enabled sufficient space to accommodate the glass materials expansion. The results show that with the incorporation of CAC, recycled glass dominated AAC mortars that contain higher than 80% total recycled glass materials can be fabricated. A residual strength increment of up to 450% can be obtained while maintaining the original dimension without expansion after the elevated temperature exposure.

This paper reports the effect of high-volume fly ash (low and high calcium types) with and without silica fume as Portland cement replacement on the heat of hydration of binary and ternary cement mixes. Both low and high calcium fly ash types were used to replace part of Portland cement at 50%, 60% and 70% by mass as binary cement mixes. The combination of fly ash and silica fume at 10% by mass as ternary cement mixes was also studied. The results indicated that low calcium fly ash retarded the rate of heat evolution more than high calcium fly ash at the same cement replacement levels. The total released heat reduction of about 70% can be achieved as Portland cement was replaced up to 70 mass% with low calcium fly ash. Total released heat of high calcium fly ash when compared to low calcium fly ash at 50%, 60% and 70% by mass of Portland cement replacement levels were higher by approximately 35%, 24% and 63%, respectively. The results confirmed that CaO content in fly ash had a significant effect on the hydration reaction of these cement mixes. In ternary cement mixes, in both low and high calcium fly ash, silica fume acted as a nucleation site that results to acceleration in the rate of heat evolution and total released heat more so than binary mix cement pastes, which contributed to the increase in early age compressive strength.

Turning waste-to-resources is one of the key scientific interests in recent years, especially within industrial symbiosis networks in order to reduce the waste management problem and associated environmental consequences, improve materials efficiency and conserve natural resources. Considering global concern over fossil fuel burning and CO2 emission, engineered fuels are increasingly used in cement production. The techno-environmental feasibility of using post-consumer wood derived fuel (WDF) in practical application is rarely reported. This study comprehensively evaluated the process feasibility and environmental compliances of utilizing WDF as an alternative fuel in the co-combustion process. The results revealed that physical parameters of WDF met the required fuel standards, and the air emissions by continuous emission measurements also met the specified limits and comparable to the baseline. The stack emission parameters monitored including particulates, dioxin, mercury, cadmium and thallium, and other heavy metals were about 60%, 2%, 21%, 6% and 7% of the specified limits. In addition to significantly reducing CO2 emission (16% for using 20% WDF as co-fuel), the characteristics, of the flue gas as monitored by continuous emission monitoring and periodic stack emission at the cement plant, and the produced clinker quality were also not affected by the use of WDF. These have demonstrated the suitability of WDF as co-fuel for cement production.

Municipal solid waste incinerator fly ash (IFA) is categorized as a hazardous waste, which requires proper treatment prior to landfilling due to its high concentrations of toxic elements. This study developed an innovative and cleaner method for stabilization/solidification (S/S) of IFA by the incorporation of supplementary cementitious materials (SCMs) and green stabilizers. Quantitative X-ray diffraction and thermogravimetric analyses indicated that toxic elements in IFA inhibited the cement hydration. Therefore, the single use of cement (10 wt%) was not efficient for the immobilization of toxic elements, especially for Pb. The incorporation of SCMs (20 wt% of binder) such as silica fume facilitated the formation of additional cement hydrates and reduced Pb leachability by 36.3%. The addition of green stabilizers such as potassium dihydrogen phosphate (KDP) and wood waste-derived biochar also improved the immobilization of toxic elements. KDP directly combined with Pb2+ to form a precipitate of Pb3(PO4)2, whereas biochar promoted the generation of cement hydrates for S/S via the effect of internal curing. The incorporation of silica fume (40 wt%) in the binder was the most effective. Overall, this study demonstrated that the selected green binders can serve as low-carbon and high-efficient material for S/S of hazardous ash residue such as IFA.

Stabilization/solidification (S/S) is a low-cost and high-efficiency remediation method for contaminated soils, however, conventional cement-based S/S method has environmental constraints and sustainability concerns. This study proposes a low-carbon, cement-free, clay-based approach for simultaneous S/S of As and Pb in the contaminated soil, and accordingly elucidates the chemical interactions between alkali-activated clay binders and potentially toxic elements. Quantitative X-ray diffraction and 27Al nuclear magnetic resonance analyses indicated that the addition of lime effectively activated the hydration of kaolinite clay, and the presence of limestone further enhanced the polymerization of hydrates. X-ray photoelectron spectroscopy showed that approximately 19% of As[III] was oxidized to As[V] in the alkali-activated clay system, which reduced toxicity and facilitated immobilization of As. During the cement-free S/S process, As and Pb consumed Ca(OH)2 and precipitated as Ca3(AsO4)2·4H2O and Pb3(NO3)(OH)5, respectively, accounting for the low leachability of As (7.0%) and Pb (5.4%). However, the reduced amount of Ca(OH)2 decreased the degree of hydration of clay minerals, and the pH buffering capacity of the contaminated soil hindered the pH increase. Sufficient dosage of lime was required for ensuring satisfactory solidification and contaminant immobilization of the clay-based S/S products. The leachability of As and Pb in high-Ca S/S treated soil samples was reduced by 96.2% and 98.8%, respectively. This is the first study developing a green and cement-free S/S of As- and Pb-contaminated soil using clay minerals as an environmentally compatible binding material. Keywords: Green/sustainable remediation, Low-carbon contaminant immobilization, Calcined clay, Alkali-activated materials, Waste valorization/recycling, Arsenic/lead leachability

A coupled CO2-water curing regime was employed on Ordinary Portland cement (OPC) paste samples immediately after casting, which allowed carbonation and hydration of OPC to proceed simultaneously. The strength development and microstructural evolution was evaluated by using multiple-techniques. The results indicated that, compared to the normal hydrated counterpart, a lower porosity, higher amorphous phase content and overall reaction degree can be achieved in the coupled CO2-water cured OPC sample. By combining with the morphological observations, a new mechanism was proposed for the rapid hardening of OPC. It is shown that the carbonation reactions led to the formation of calcite particles, which provided more nucleating sites for C S H gel growth; and thus, an increase in the overall reaction degree of the cement paste can be achieved within the first 24 h compared to the conventional water curing process.

Many studies have focused on the feasibility of using nanoparticles including nanoalumina (NA), in cement composites and reported some positive effects on the properties of concrete. However, there are still uncertainties about the effects of NA addition on cement hydration. In this study, γ-NA particles with a size of about 30 nm was incorporated into Portland cement pastes and the physicochemical and microstructural properties of the NA-modified cement pastes were analyzed. Conduction calorimetry results showed that NA accelerated the silicate and aluminate phases reactions in OPC. Compared to the plain cement paste, the NA-modified cement pastes exhibited improved compressive strength at all ages due to the reduced macropores and the accelerating effect on cement hydration induced by NA, but the strength enhancement at 28 days was less obvious. Moreover, back scattering electron imaging and energy-dispersive spectroscopy (BSE-EDS) analysis indicated that the Al-enriched outer C-S-H formed in the NA modified paste; and it was mainly due to the NA particles acting as seeding for the growth of the outer C-S-H at the early age, rather than the Al released by the aluminate phases. This also provided a possible explanation for the substantial increase in CH and chemical bounded water contents in the NA-modified pastes at 12 h, but almost no change at 28 days of hydration.

The present work is focused on the effect of particle size of silica on its early age reactivity and its impact on C-S-H microstructure and mechanical strength at the early and later ages of hydration. Two different types of commercially available silica i.e. Elk-microsilica (Elk-Si) (100–300 nm) and colloidal nanosilica (CNS) (8–15 nm) were used for the study. The lime silica reaction was carried out with a C/S ratio 2.0 and the reaction was monitored in the first 24 h with a range of instrumentation techniques. The results showed that the CNS had ∼60% higher reactivity than the Elk-nSi. Calorimetric results revealed that in the presence of CNS, the hydration rate and the formation of AFm phase were accelerated. Furthermore, FTIR and NMR results revealed that in the presence of the CNS, the structure of C-S-H gel was also affected. This acceleration and modification C-S-H gel led to the formation of a compact microstructure as the capillary porosity of cementitious system measured by MIP was found to reduce significantly. The formation of a compact microstructure at the early age of hydration improved the early age mechanical strength. However, it hindered the later age hydration and thus more unhydrated cement was observed in the semi-quantitative XRD and BSE/IA analysis, especially in the presence of higher dosages of CNS, which was responsible for the lower long term mechanical strength.

In this study, municipal solid waste incineration bottom ash (MSWIBA) and waste glass were recycled and reused to synthesize aerated or cellular alkali-activated concrete (AAAC) in order to minimize their disposal at landfills and to produce a value-added construction material. The experimental results showed that incorporating 20% waste glass powder (WGP) in the alkali-activated MSWIBA-WGP products would not cause a decrease in strength, and WGP can be considered as a precursor as well as a waste-derived activator to provide the reactive silica for geopolymerization. The MSWIBA as the main precursor contributed to the structure forming of AAAC as well as acting as a source of foaming agent due to the presence of metallic aluminium. The prepared AAAC incorporating 20% WGP exhibited low thermal conductivities ranging from 0.14 to 0.38 W/m·K with compressive strengths ranging from 0.9 to 10.4 MPa, and density values from 494 to 1295 kg/m3. The results obtained by optical photography and Scanning Electron Microscopy-backscattered electrons imaging methods showed that the prepared AAAC had less spherical air voids and wider air-void size distribution from 0.02 to 3.0 mm when compared to traditional aerated cement concrete, and the reactive silica was able to form C(N)-A-S-H which provided the mechanical strength development of AAAC.

Waste timber formwork from construction sites was used as fibre to prepare wood-magnesium oxychloride cement (MOC) board. The effect of wood fibre content, pulverized fly ash (PFA) and incinerated sewage sludge ash (ISSA) on the mechanical and durability properties of wood-MOC board was investigated. Greenhouse gases (GHGs) emission, one of the representative and most globally concerned environmental impacts, for the production of different types of composite boards was assessed and compared by using lifecycle assessment (LCA) technique. The ‘cradle-to-gate’ system boundary with 1 kg of board production was considered as the functional unit in this assessment. The result showed that the wood-MOC composites prepared with a higher content of wood fibre had a lower thermal conductivity, higher flexural strength, higher residual flexural strength after exposure to high temperatures and water immersion, and better noise reduction effect. Even though the water absorption was increased with the increase of wood fibre content, it can still be considered to be low. The wood -MOC composites incorporating ISSA showed higher flexural strength, better high temperature resistance and better water resistance than other composites. In addition, the production of the wood MOC board induces lower GHGs emission than plywood and lower human toxicity than conventional resin-based particleboard.

Stabilization/solidification (S/S) is a low-cost and time-efficient method for soil remediation, however, delayed hydration reactions and high carbon footprint are major limitations for the treatment of high-Pb contaminated soil. This study develops a novel and low-carbon approach that combines ground granulated blast furnace slag (GGBS) and ordinary Portland cement (PC) with phosphate-/sulphate-rich byproducts to produce low-alkalinity, high-compatibility, high-strength binary cement (BC) for S/S process. Results show that contaminated soil with a large fraction of exchangeable and soluble Pb (e.g., shooting range sites) severely disturbed the formation of hydration products in conventional S/S treatment, whereas BC system could mitigate the Pb interference via precipitation and sorption evenly distributed on the BC hydrates as shown by elemental mapping. Thus, BC presented superior environmental performance in terms of toxicity characteristic leaching procedure (TCLP) and semi-dynamic leaching tests, which were substantiated by quantitative X-ray diffraction and thermogravimetric analyses. The addition of potassium dihydrogen phosphate reduced TCLP leachability of Pb by 86.9% and Pb diffusion coefficients by 69.4% due to the formation of insoluble Pb3(PO4)2. Similarly, incinerated sewage sludge ash enhanced Pb stabilization, whereas waste phosphogypsum increased early strength via precipitation of PbSO4, although the effectiveness of physical encapsulation was compromised due to reduction in hydration products. Therefore, the proposed binary binders with selected additives present a new and low-carbon S/S treatment for high-Pb shooting range soil remediation.

Urban solid waste disposal has become a global concern due to the huge waste volume and its adverse environmental impacts. Construction and demolition waste (CDW) and municipal solid waste incinerator bottom ash (IBA) are two main urban solid waste streams that have attracted global research interest for their recycling and reutilization. It is acknowledged that cement treatment is an effective method to facilitate the wastes to be used in road subbase. In this chapter, cement-treated recycled concrete aggregates (RCAs) derived from CDW and IBA generated from MSW incinerators were evaluated and the feasibility of using the cement-treated semirigid pavement base course was explored. Additionally the environmental impact was investigated in terms of assessing the effect of the cement treatment of the blended RCA-IBA mixture on stabilizing heavy metals and reducing their leaching to the environment.

In this chapter, case-specific environmental impacts of different construction materials production in Hong Kong including cement, aggregates, concrete and concrete products were assessed by the life cycle assessment (LCA) method. For adopting the circular economy (CE) principle in the construction materials production, both open-loop and closed-loop approaches were adopted. The results of the case studies demonstrate that using waste wood for replacing fossil fuels for clinker production, and waste glass powder to replace part of the clinker material, can be effective open-loop strategies for resource saving and environmental impact reduction in cement production. While adopting an open-loop LCA approach, e.g. using supplementary cementitious materials and glass powder for replacing cement, and a closed-loop approach, e.g. using recycled aggregates for the production of concrete and concrete products, can considerably reduce environmental impacts. This chapter also describes the effective implementation of industrial ecology using LCA for reducing environmental impacts, non-renewable resources consumption, and reutilizing waste materials as secondary resources for cement and concrete production within the CE principles.

Management of incinerated sewage sludge ash (ISSA) and dredged contaminated marine sediments (CMSs) is a great challenge for Hong Kong and other coastal cities due to limited landfilling capacity. The present study investigates the use of high content (20% of sediment by mass) of ISSA in combination with cement/lime for solidification/stabilization (S/S) treatment of CMSs to provide a way to reuse the wastes as construction materials. The results showed that ISSA being a porous material was able to absorb a large amount of water rendering a more efficient solidification process of the marine sediment which normally had a very high water content (∼80%). The S/S treatment improved the engineering properties of the sediment, but reduced the workability, especially for the lime-treated samples. Lime can be used to replace ordinary Portland cement (OPC) for better heavy metal immobilization and carbon emission reduction. The hardened sediment samples prepared with 10% of lime and 20% of ISSA could attain a strength of 1.6 MPa after 28 d of curing. In addition, leaching tests confirmed that there was no environmental risk induced by these stabilized materials. The formation of hydrated cementitious compounds including calcium silicate hydrate (C–S–H)/calcium aluminate silicate hydrate (C-A-S-H)/hydrocalumite/calcite was mainly responsible for the strength development in the ISSA/lime-treated sediments.

Steel corrosion caused by chloride penetration is an important problem in construction practices threatening the long-term durability of reinforced concrete structures. In this study, the effects of blast-furnace slag on the passivation and corrosion processes of carbon steel embedded in cement pastes were investigated by electrochemical measurements, and equivalent circuit models were proposed for analysis of the passivation and corrosion processes. The spatial chloride distributions in the cement paste after corrosion initiation were determined distinguishing between amounts of total, free and bound chloride. The values of the open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements indicated that the carbon steel embedded in cement pastes was passivated due to the presence of an alkaline pore solution. However, the formation of passive layers on the surface of carbon steel in the slag-blended cement paste was weakened by the more negative OCP value due to a lower pH value and higher sulphide concentration in the pore solution. Upon initiation of corrosion during the electrical acceleration test, the OCP value dropped to a significantly more negative value whereas the Warburg impedance in the equivalent circuit model sharply decreased. Moreover, the addition of slag decreased the threshold chloride concentration at the steel surface to initiate steel corrosion. On the other hand, the enhanced resistance against chloride penetration and the higher chloride binding capacity resulted in an overall increase of the corrosion resistance of carbon steel in slag-blended cement paste.

Barium slag (BS) is a hazardous industrial solid waste formed during the production of barium carbonate. The accumulated stock of BS in China has exceeded 10 million tons, which urgently needs to be recycled in an efficient and sustainable way. BS contains a lot of soluble Ba2+ with a leaching concentration up to 2000 mg/L in water. Meanwhile, Ba2+ is an alkali-earth metal which can activate ground granulated blast furnace slag (GGBFS). This paper explores the possibility of incorporation BS as an admixture for alkali activated slag (AAS) cement. The mechanical property and microstructure evolution of AAS pastes with addition of BS are investigated in comparison with pure AAS paste. The results indicate that the addition of BS could significantly enhance mechanical strength of AAS paste, attributing to the increased hydration degree and the formation of dense pore structure. In addition, the leaching concentration of Na+ shows a significant decline by incorporation of BS in AAS paste, associated with the changed composition of hydration products. Therefore, BS is a promising admixture for AAS cement and holds great potential for promotion and application.

Finding suitable disposal sites for dredged marine sediments and incinerated sewage sludge ash (ISSA) is a challenge. Stabilisation/solidification (S/S) has become an increasingly popular remediation technology. This study sheds light on the possible beneficial use of ISSA together with traditional binders to stabilise/solidify marine sediments. The performance of the binders on S/S of sediment 1 (clean) and sediment 2 (contaminated) was also compared. The results showed that the use of ISSA as part of the binder was effective in promoting the strength of the sediment with a high initial moisture content due to ISSA porous and high water absorption characteristics. The sediments treated with 10% cement and 20% ISSA attained the highest strength. Also, cement hydration as well as pozzolanic reactions between ISSA and Ca(OH)2 made contributions to the strength development. This was supported by the microstructural analysis, in particular the porosity results. In terms of environmental impacts, two leaching tests (toxicity characteristic leaching procedure and synthetic precipitation leaching procedure) found that all the S/S treated sediment by 10% lime and 20% ISSA resulted in the lowest leachate concentrations under the on-site reuse scenario or under simulative acidic rainfall conditions. Therefore, recycling waste ISSA with lime can be used as an appealing binder to replace cement to stabilise/solidify dredged marine sediments for producing fill materials.

Mortar made from concrete slurry waste (CSW) and municipal solid waste incineration bottom ash (MSWIBA) could be recycled into cold bonded lightweight aggregates (CBLA). However, the mechanism by which the CSW-MSWIBA mortar hardened and developed strength remains unexplored. Furthermore, the investigation in the previous study was limited to using the CBLA for wet precast lightweight concrete (LWC). Understanding the characteristic of CSW-MSWIBA mortar and exploring a new application of CBLA can promote the larger-scale recycling of CSW and MSWIBA. Herein, an investigation was performed on assessing the multi-component characteristics of CSW-MSWIBA mortar. The results showed that using MSWIBA (i.e., as compared to river sand) in CSW was advantageous for lower density and higher compressive strength of the mortar. The strength development of hardening CSW-MSWIBA mortar could largely be ascribed to the continuous cement hydration of CSW and the pozzolanic reaction between MSWIBA and CSW providing a better bonding at the CSW-MSWIBA interface. Following a pelletization process, the CSW-MSWIBA mortar was turned into cold bonded lightweight aggregates (CBLA). Through a trial of industrial-scale production, the CBLA were then used to fabricate semi-dry precast LWC, which met the LWC and masonry unit requirements as per BS EN 206 or JGJ/T 12 and BS 8103, respectively.

Coastal cities like Hong Kong rely heavily on their coastal and marine infrastructure for social-economic development. A major challenge for marine infrastructure is steel corrosion, which is the main cause for infrastructure deterioration. Also, fresh water is a scarce resource for some remote islands, and to meet the water requirement for concrete preparation in these regions, seawater is increasingly being considered as an alternative which would inevitable aggravate the deterioration problem due to steel corrosion. Up to now, a number of studies have focused on the effects of seawater on the workability, mechanical strength and durability (in particular corrosion of steel reinforcement) of cement pastes and reinforced concrete. However, the understanding on the influence of seawater on the composition and microstructure of cement hydration products is limited. This paper presents a preliminary study on the effects of individual salt components of seawater on the hydration process of C3S. The microstructure changes of the hydration products were also studied. The mechanism of the acceleration effect is analyzed. Na+ and Mg2+ can affect the dissolution of C3S and the participation of the hydration products. For the later age, Mg2+ can substitute part of Ca2+ and change the composition of the final reaction products.

Navigational dredging is an excavation of marine/freshwater sediment to maintain channels of sufficient depth for shipping safety. Due to historical inputs of anthropogenic contaminants, sediments are often contaminated by metals/metalloids, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and other contaminants. Its disposal can present significant environmental and financial burdens. This study developed a novel and green remediation method for contaminated sediment using stabilization/solidification with calcium-rich/low-calcium industrial by-products and CO2 utilization. The hydration products were evaluated by quantitative X-ray diffraction analysis and thermogravimetric analysis. The incorporation of calcium carbide residue (CCR) facilitated hydration reaction and provided relatively high 7-d strength. In contrast, the addition of Class-F pulverized fly ash (PFA) and ground granulated blast furnace slag (GGBS) was beneficial to the 28-d strength development due to supplementary pozzolanic and hydration reactions. The employment of 1-d CO2 curing was found to promote strength development (98%) and carbon sequestration (4.3 wt%), while additional 7-d air curing facilitated cement rehydration and further carbonation in the sediment blocks. The leachability tests indicated that all studied binders, especially CCR binder, effectively immobilized contaminants in the sediments. The calcium-rich CCR and GGBS were regarded as promising candidates for augmenting the efficacy of CO2 curing, whereas GGBS samples could be applicable as eco-paving blocks in view of their superior 28-d strength. This study presents a new and sustainable way to transform contaminated sediment into value-added materials.

This study presents experimental results in an attempt to explain why photocatalytic cementitious materials prepared with white cement (WC) had superior photocatalytic NOx removal performance than those prepared with ordinary Portland cement (OPC). The UV–Vis diffuse reflectance spectra (DRS) of dry WC and OPC demonstrated that OPC had a stronger light absorption ability. And electrochemical impedance spectroscopy (EIS) analysis revealed that OPC incurred higher charge transfer resistance on the inter-surface of OPC and TiO2. Moreover, the OPC/P25 dry mixtures displayed a relatively lower photoluminescence (PL) intensity at 420 nm. The addition of iron oxide (Fe2O3) in WC caused a decrease in NOx removal, a boost in light absorption, an increase in the resistance of charge transfer, and a reduction in PL intensity. Collectively, the relatively poor performance of OPC/P25 mixtures in photocatalytic NOx removal is due to a combination of stronger light absorption and lower charge separation caused by OPC.

Incineration is used to manage sewage sludge in many countries and regions including Hong Kong. This generates a huge amount of incinerated sewage sludge ash, the disposal of which is an environmental issue. In this research, an eco-friendly cementitious binder was developed by adding 10, 20, and 30 wt % of lime into sludge ash to obtain different lime/sewage sludge ash ratios. The same amounts of ordinary Portland cement were also added to the equivalent batches of sewage sludge ash for comparing the two systems. Paste samples were characterised for heat of hydration, mechanical properties and thermogravimetric analysis. Microstructural analysis using X-ray diffraction and scanning electron microscopy and the factors controlling strength development are reported. The results show that sewage sludge ash accelerated the hydration rate of cement, and the lime pastes with sewage sludge ash showed larger amounts of heat and higher reactivity than the cement pastes with sewage sludge ash. Considering the lime-based binder was mainly proposed for the production of controlled low strength materials, within the lime system the optimum mechanical properties (compressive strength) were achieved by the 30% lime with sewage sludge ash mix and the strength value showed remarkable improvement from 28 to 90 days of curing. The crystalline phases responsible for the strength development in the lime-based system were mainly brushite and calcium phosphate hydrates. The lime with sewage sludge ash mix has potential to be used for the development of new controlled low-strength materials.

Poor early-age performance (e.g. lower early strength, longer setting time) is an important technical challenge for the application of blended cementitious materials containing low reactivity or high volumes of supplementary cementing materials. In this study, the mechanism of using nanosilica (NS) to improve the early-age properties for cement mortars blended with glass powder (GP) and glass aggregates has been investigated. The results indicate that the addition of NS into glass-based cement mortar largely improved the early stiffening which was dependent on high specify surface area of the NS rather than cement hydration. Combining the use of NS and GP was conducive to compensate the delayed setting times and the strength losses caused by the incorporation of GP. These beneficial behaviors were associated with the physical, acceleration, pozzolanic and pore refinement effects of NS. In terms of heat of hydration, the inclusion of NS intensified and accelerated the appearance of the third exothermic peak (AFt to AFm) due to the absorption of sulfate ions by the increased C-S-H formation. Also, the total hydration heat liberated was found to correlate linearly with the corresponding early-age compressive strength. Microstructural analysis suggest that NS significantly helped to densify the microstructure of the GP blended cement matrix and improved the interface between the GP particle and the binder matrix. This was verified by the contribution of NS on refining the coarse pore size caused by the use of GP as a replacement of cement.

Fine municipal solid waste incineration bottom ash (MSWIBA) contains more contaminants (e.g. metallic aluminium, glass and gypsum) that cannot be effectively removed by current recycling techniques and this thus limits its engineering application in concrete products. Instead of removing these contaminants, the objective of this research was to investigate the influences of using different casting methods and various supplementary cementitious materials (SCMs) on improving the properties of cement mortar prepared with the fine MSWIBA. In this study, the mortar bar specimens incorporating 100% fine MSWIBA as sand were prepared using the conventional wet-mixed method and a dry-mixed method. The SCMs applied were fly ash (FA), ground-granulated blast-furnace slag (GGBS) and waste glass powder (GP), with a replacement ratio of 30 wt% of ordinary cement in the mortar. The curing conditions of the specimens were in the 20 °C water, in the 80 °C water and in an 80 °C NaOH solution for 28 days, respectively. The experimental results showed that the dry-mixed method was an effective method to mitigate the expansion of the mortar prepared with MSWIBA as well as to enhance its mechanical properties after being subjected to the NaOH solution. The order of effectiveness of SCMs on the reduction in the expansion of the mortar prepared with MSWIBA was FA, GGBS and GP. It was indicated that FA was the most effective in mitigating the alkali-silica expansion as well as the alkaline-Al reaction.

The water resistance of magnesium oxychloride cement (MOC) incorporating glass powder (GP) and pulverized fuel ash (PFA) with and without CO2 curing was investigated in terms of the strength retention coefficient and the volume stability. The microstructure was studied using quantitative X-ray diffraction (QXRD), thermogravimetry (TG), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the effect of incorporating GP on the water resistance is much lower than that of PFA due to the lower pozzolanic activity of GP generating a lower amount of magnesium silica hydrate gel (M-S-H gel). The MOC incorporated with GP or PFA showed high water resistance after CO2 curing due to the higher quantity of amorphous gel that formed a much denser interlocking network.

As the world’s most widely used construction material, the production of concrete has been recognized to lead to major environmental impacts. To promote sustainability in the concrete industry, various kinds of supplementary cementitious materials (SCMs), such as fly ash, blast furnace slag and silica fume have been used to replace cement in concrete production. The nature of these SCMs has therefore been changed from wastes to co-products or by-products. Life cycle assessment (LCA) has been increasingly adopted in the concrete industry to assess environmental sustainability. However, the choice of an appropriate method for impact distribution in the LCA of concrete incorporating SCMs is a research challenge. This study aimed to present a comprehensive review of the impact allocation approaches for assessing the environmental impacts of SCMs-incorporated concrete. Furthermore, the use of the system expansion approach was compared with the conventional mass and economic allocation approaches. A case study of concrete production using SCMs in Hong Kong was conducted using the different approaches. The results were then analyzed and it was concluded that the system expansion approach is appropriate for the assessment of the environmental impacts of SCMs-incorporated concrete.

This paper presents a study on alkali activated cement (AAC) mortar produced with waste soda-lime-silica glass. The waste glass was used simultaneously as a precursor and fine aggregates in the alkali activated fly ash-slag mortar. The influences of waste glass in cullet and powder forms on workability, compressive and flexural strengths, fire resistance of the AAC mortar were investigated. The experimental results showed that the workability was gradually increased as the replacement level of natural sand by glass cullet was increased, and it was significantly improved with decreasing aggregates-to-binder ratios. The mechanical properties data indicated that the compressive strength was reduced as the glass cullet content increased. However, for the flexural strength, the optimum percentage of glass cullet replacement was 50%. Due to the low reactivity, a reduction in strength was observed when the glass powder was used to replace the fly ash and slag. Nevertheless, in terms of fire resistance, the incorporation of glass cullet could improve the resistance of the AAC to high temperature exposures (800 °C). In particular, the AAC mortar prepared with the glass powder as a precursor exhibited remarkable resistance to high temperature. The use of waste glass in AAC material was feasible from the mechanical properties and fire resistance points of view.

Upcycling contaminated wood waste by magnesia-phosphate cement (MPC) into rapid-shaping cement-bonded particleboards is a promising technology. MPC binder exhibited superior compatibility with wood waste. However, there is a need to address the limitations of high brittleness, low strain capacity, and low water resistance of MPC products. High content of recycled wood in the MPC particleboards (20 wt%) should be accomplished without compromising their mechanical strength and durability. In this study, the addition of 2% (v/v) polyvinyl alcohol (PVA) fibre significantly reinforced flexural strength and fracture energy of particleboards, as high as 56.5% and 891.9%, respectively. The characteristics of PVA fibre determined the efficiency of reinforcement. At the same dosage, addition of shorter fibre (3 mm in length) presented higher strength, whereas incorporation of longer fibre (12 mm) improved fracture energy. Thinner fibre (35 µm in diameter) showed a larger increase in both flexural strength and fracture energy. Surface morphology of PVA fibre played an important role in determining the reinforcement mechanisms and reinforcing efficiency. Under stress, hydrophobic fibres (oil-treated) were pulled out from MPC matrix, whereas hydrophilic fibres (untreated) were ruptured. The former showed higher reinforcing efficiency for MPC particleboards. The fibre-reinforced particleboards maintained sufficient mechanical strength and dimensional stability after 24-h water immersion or 1-h heating at 100 °C, which fulfilled the standard requirements. This study demonstrated that PVA fibre addition is an effective method to reinforce mechanical properties as well as thermal and water resistance of MPC particleboards.

An alternative CO2 curing method for precast concrete products has been proposed in order to achieve rapid strength development at early age, as well as to capture and store greenhouse gas (CO2). In this paper, an experimental study for the development of a maturity approach is presented to estimate the strength development of carbonated concrete blocks. In order to promote the use of industrial flue gas containing CO2, a flow-through CO2 curing regime at ambient pressure and temperature was employed using different atmospheric conditions, such as various CO2 concentrations, RH values and gas flow rates. The experimental results showed that the compressive strength or maturity of the carbonated concrete blocks was affected by two factors: accelerated cement hydration and carbonation extent. A high CO2 concentration, a fast gas flow rate and a moderate relative humidity were essential for enhancing the maturity and the strength development. The developed model based on the maturity approach may accurately predict the strength development of the carbonated concrete blocks.

Concrete paving blocks are widely used in many parts of the world because of their flexibility in construction and low maintenance costs. New generations of the blocks have already incorporated some types of wastes for achieving waste recycling. Sewage sludge ash (SSA) produced from the incineration of dewatered sewage sludge may be used to partially replace cement for construction. This study investigated the properties of concrete blocks using SSA as a cement replacement together with recycled construction and demolition aggregates or glass cullet (GC) as a partial substitution of natural aggregates for producing concrete blocks by the dry mix (zero slump) compression method. No research in published literature has been conducted on the complementary effects from the utilization of SSA as a cement substitute and some recycled materials as aggregates in producing concrete blocks. Assessments of technical benefits and leaching risks were made with a view to encouraging recycling of waste materials and enhancing conservation of natural resources. The research findings revealed that the SSA possessed moderate pozzolanic activity and it increased the long term compressive strength of the blocks. More importantly, it was found that combining the use of SSA with GC is superior to using the ash alone for block making due to significant reduction in drying shrinkage. On the other hand, the alkali-silica reaction caused by the reactive GC could in turn be suppressed with the incorporation of the SSA. Leaching tests conducted also showed compliance with the regulatory limits. These results indicate that the combined use of SSA and GC can produce paving blocks with satisfactory mechanical, durability and leaching properties while helping the recycling of the two types of solid wastes.

The disposal of large amount of waste glass at landfills has increasingly posed an environmental issue in Hong Kong. This study focused on recycling of waste glass cullet and powder into cement mortar products. The physical and chemical evolutions of cement pastes prepared with glass powder and fly ash subjected to elevated temperatures and loading were evaluated. The residual strength of the cement pastes was determined after cooling and the microstructure was analysed from mineralogy and morphology views. The improvement of the residual compressive strength was noticeable after 800°C exposure thanks to the incorporation of glass power in the cement pastes. The results showed that a new crystalline phase, devitrite (Na2Ca3Si6O16), was formed from the softened amorphous silica of the glass powder, which might contribute to improving the residual compressive strength. This was also confirmed by the observation that pores and micro cracks of the cement pastes were filled after 800°C exposure. By means of positive effect of the glass power in improving the high temperature resistance of cement-based materials, dry-mix cement mortars were designed with the glass powder as a replacement of cement and the glass cullet as a replacement of natural aggregates for testing the compressive strength at 800°C ("hot test"). The use of the glass powder and the glass aggregates in mortars could both improve the high temperature resistance. However, excessive use of glass materials softened the mortars, which could not sustain high temperature loadings. The contents of the glass powder and the glass aggregates should be cautiously controlled to balance the two opposing effects.

The generation of dredged sediments (DS) exerts a heavy burden on the surrounding environment. Traditional landfills of DS not only contaminate the environment, but also waste precious resources. In this study, DS from Taihu Lake, together with calcium carbide slag (CCS) and ground granulated blast-furnace slag (GGBS), was used as supplementary cementitious materials (SCM) to replace cement to develop a novel cementitious binder for the production of mortar. The effects of varying contents of DS, CCS, and GGBS on the properties of the specimens were systematically investigated. The results showed that the incorporation of DS in cement mortar led to a reduction in the flexural and compressive strength at all curing ages in a dosage dependent manner due to a rather weak pozzolanic activity. The addition of GGBS in the specimen significantly increased the 28-d flexural and compressive strength, which was even higher than that of the samples with the same amount of cement. More importantly, this beneficial effect was more obvious in the co-existence of GGBS and CCS because of the formation of more C-S-H gel (with a simultaneously high pH) revealed by XRD, SEM and TG analysis. The optimum mechanical properties were obtained by a combination of 60% OPC, 20% DS, 10% GGBS, and 10% CCS. Whereas, the mix with a higher content of DS (20% OPC, 60%DS, 10% GGBS and 10% CCS) can be potentially used for controlled low-strength materials. The application of the developed product in eco-friendly construction materials can sustainably alleviate the burden of DS, CCS, and GGBS on the environment.

To transform construction wood waste by magnesia-phosphate cement (MPC) into cement-bonded particleboards, instability of MPC in water that compromises durability of particleboards in moist environment needs to be addressed. This study proposed a novel use of alumina and red mud to improve water resistance of MPC particleboards. Cement hydration chemistry and microstructure characteristics were revealed by quantitative X-ray diffraction analyses and scanning electron microscopy. Addition of alumina or red mud (Mg/Al or Mg/Fe at optimal molar ratio of 10:1) facilitated formation of amorphous MgAl or MgAlFe phosphate gel, respectively, which enhanced compressive strength. Alumina improved short-term water resistance, whereas red mud provided better long-term water resistance. Red mud-MPC binder enhanced strength retention (by 22.8%) and reduced water absorption (by 26.4%) of particleboards after 72-h water immersion, probably attributed to stable scaly-like MgAlFe phosphate gel. This study demonstrated that red mud and wood waste are sustainable materials for producing particleboards.

This study designed a novel cement-based architectural tile prepared with more than 70% waste glass content (by weight). The waste glass was employed not only as decorative aggregates but also as a supplementary cementitious material in the architectural mortar. In terms of shrinkage, the incorporation of glass powder (GP) could significantly reduce the drying shrinkage of the glass mortars regardless of its fineness. When the glass mortars were subjected to high temperature (800 °C), the inclusion of GP into the mortars was more able to mitigate the flexural and compressive strengths losses as compared to the control glass mortar prepared without the use of GP. Furthermore, using the GP and glass aggregates simultaneously could effectively improve the resistance of the glass mortars to sulfuric acid attack and the positive effect was more pronounced when finer GP was incorporated. In particular, an encouraging result shows that the replacement of 20% cement by fine GP successfully suppressed the deteriorative alkali-silica-reaction (ASR) expansion caused by the glass aggregates. Also, the glass mortars incorporated with fine GP exhibited comparable or even superior durability properties than that of the fly ash blended glass mortar. Keywords: Glass powder, Glass aggregates, Durability, Architectural mortar

Sewage sludge ash (SSA) is the byproduct obtained from incinerating mechanically dewatered sewage sludge. Some published literature mentions that mortars of comparable strength can be produced using a small amount of SSA to replace cement. However, information on how SSA affects the properties of cement mortars is limited given the pozzolanic activities of most SSA being modest. This study identified the mechanisms behind some beneficial effects of the SSA on the strength development of mortars through a comparison study with fine sewage sludge ash (FSSA) and pulverized fly ash (PFA). The findings of this study indicated that the presence of SSA accelerates the rate of heat evolution from cement hydration while PFA does not produce this effect. A higher content of SSA or FSSA produces a greater effect. Replacing cement by SSA or FSSA up to 10% did not induce significant changes to the pore structure of the pastes. The formation of brushite in SSA or FSSA cement mortars contributes to the long-term strength of the mortars. PFA reduces the drying shrinkage of the mortars, but SSA causes greater drying shrinkage due to increasing content of mesopores with sizes less than 0.025 µm. This harmful effect is greater with FSSA.

Cement-based stabilization/solidification (S/S) is a practical treatment approach for hazardous waste with anthropogenic As sources; however, its applicability for geogenic As-containing soil and the long-term leaching potential remain uncertain. In this study, semi-dynamic leaching test was performed to investigate the influence of S/S binders (cement blended with fuel ash (FA), furnace bottom ash (FBA), or ground granulated blast furnace slag (GGBS)) on the long-term leaching characteristics of geogenic As. The results showed that mineral admixtures with higher Ca content and pozzolanic activity were more effective in reducing the leached As concentrations. Thus, cement blended with FBA was inferior to other binders in suppressing the As leaching, while 20% replacement of ordinary Portland cement by GGBS was considered most feasible for the S/S treatment of As-containing soils. The leachability of geogenic As was suppressed by the encapsulation effect of solidified matrix and interlocking network of hydration products that were supported by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) results. The long-term leaching of geogenic As from the monolithic samples was diffusion-controlled. Increasing the Ca content in the samples led to a decrease in diffusion coefficient and an increase in feasibility for "controlled utilization" of the S/S-treated soils.

An experimental study was carried out to evaluate the mechanical and durability properties of architectural mortar prepared with 100% glass aggregates and using supplementary cementitious materials (SCMs) to replace cement. The mechanical properties were assessed in terms of compressive and flexural strength, whilst the durability characteristics were investigated in terms of drying shrinkage, resistance to high temperature exposure, alkali-silica-reaction (ASR) and acid dissolution. Experimental results suggested that strengths of glass-based architectural mortar incorporating SCMs (fly ash, ground granulated blast-furnace slag, metakaolin and waste glass powder) were comparable or even superior to that of the pure cement mortar when the cement replacement levels was up to 20%. In particular, waste glass powder (GP) as a pozzolanic material performed better than the other SCMs for flexural strength development of the glass-based mortar. The durability results also indicated that the addition of the SCMs could significantly reduce the drying shrinkage of the glass-based architectural mortar. All the recycled glass architectural mortars prepared with SCMs showed favorable resistance to expansion due to the ASR and less strength loss after heating to 800 °C. GP and ground granulated blast-furnace slag (BS) blended mortars gave better performance below 600 °C as compared to fly ash (FA) and metakaolin (MK) blended mortar. Also, the glass-based mortar containing GP exhibited the best performance of resistance to acid attack. Therefore, there is a potential to produce high performance architectural mortars with excellent mechanical and durability properties by reutilizing recycled glass to fully replace natural aggregates and partially replace cement.

Quarry dust, a by-product of stone grinding, cutting, sieving and crushing, is abundantly available and can create many on-site and off-site environmental problems. This paper investigates the feasible utilization of quarry dust as an alternative to river sand in the production of lightweight foamed concrete (LFC). LFC with a density of 1300 ± 50 kg/m3 and fixed cement/filler ratio of 1:1 were adopted in this study. Quarry dust was used to replace sand at ratios of 75% and 100%, and four different water-to-cement ratios (w/c) of 0.52, 0.54, 0.56 and 0.58 were studied and compared. For a given w/c ratio, it was found that the use of high volume quarry dust could reduce the fluidity and increase the compressive strength and the thermal conductivity of LFC. However, no significant decrease of compressive strength was observed with the increase of w/c ratio, probably due to the reduction of foam volume requirement in the system. Life cycle assessment results indicated that the LFC containing quarry dust possessed less environmental impact in terms of lower energy consumption and lesser amount of greenhouse gases emission.

The aim of this research was to study the production of calcium sulfoaluminate-belite (CŜAB) cement from industrial waste materials via hydrothermal-calcination process. Lignite fly ash and bottom ash were used as starting materials for comparison. Other waste materials viz., Al-rich sludge and flue gas desulfurization gypsum were also key players in raw mixes for the synthesis of CŜAB cement. For lignite fly ash as a starting material, mixed phases between ye'elimite and larnite were obtained, whereas for lignite bottom ash as starting material, only ye'elimite was obtained The hydration reaction was studied in terms of heat evolution, setting time, compressive strength and hydration product formation with various gypsum contents. The results showed a rapid formation of ettringite as a main hydration product mixed with calcium silicate hydrate, monosulfate and stratlingite phases as minority, with a fast final setting time of 24–26 min and high early compressive strength of 16.0 and 18.0 MPa in 1 day for CŜAB cements made of fly ash and bottom ash, respectively.

In this work, a two-step wet carbonation process was developed to synthesize amorphous nano-silica by extracting the silicon phase from recycled cement fines (RCF), aiming to convert RCF into value-added products and sequester CO2. The phases evolution and their microstructure during carbonation were investigated. The results indicated that the RCF was carbonated rapidly to form a mixture of calcite and amorphous silica gel, followed by the formation of silica bearing gel containing aluminosilicate gel and silica gel after two-step wet carbonation. An amorphous silica with a purity of 98.8% and in the form of aggregated nanoparticles (

The incorporation of conventional supplementary cementitious materials (e.g. fly ash) in concrete generally induces a longer setting time and inferior early-age strength. This study aims to evaluate the effectiveness of using seawater (SW) as mixing water in improving the early-age properties of cement pastes/mortars prepared with waste glass powder (WGP) which has a low reactivity. By means of measurements of rheological behaviors, macro/micro mechanical properties, hydration kinetics of the WGP blended cement with SW, and other microstructural analytical techniques, the early-age performances were investigated. The results showed that the incorporation of WGP increased yield stress and plastic viscosity of the cement paste due to its fine particle size, negative surface charge and hydrolysis effect. The use of SW further changed the rheological properties by accelerating the hydration of cement. The dissolved ions from the WGP and the presence of SW in the cement paste were beneficial to shortening the prolonged setting time induced by the replacement of cement by the WGP. The combined use of SW was effective in overcoming the inferior early-age strength caused by the dilution effect of WGP inclusion at the very early age. The enhanced precipitation of hydration products, increased degree of hydration, refined pore structure were responsible for the increase of the early-age strength of the WGP blended cement prepared with SW.

An extensive amount of work has focused on investigating the effects of seawater as mixing water on the mechanical properties and durability issues of cement pastes/mortars/concrete especially with steel rebars. However, limited information was available for the effects of seawater on the microstructural properties and compositions of blended cement systems. Sewage sludge ash has been widely studied as a supplementary cementitious material to manage wastes more sustainably and to relieve the environmental burden. Therefore, this paper investigated the mechanical properties as well as the microstructural findings of the lime-sewage sludge ash binder under the effects of the most dominant ion (i.e. Cl−) in seawater by mixing with NaCl and MgCl2 (major salts of seawater) solution respectively. The results reveal that as compared to the control, acceleration effects were remarkable in the NaCl mix and the total amount of heat evolved was increased by mixing with both single salts. The use of the concerned sea salts accelerated the setting and increased the compressive strength until curing for 28 days. But for the mix prepared with MgCl2, its strength was still significantly improved at 60 days. The formation of Friedel's salt in the mix prepared with NaCl was evidenced by X-ray diffraction and thermal gravimetry mainly due to the highest concentration of Cl− in NaCl. Also, the average pore diameter was decreased, and the finer fraction of pores was increased after the addition of NaCl and MgCl2, explaining their high strengths.

Slag-cement–bentonite (SCB) slurry has been widely used for the construction of vertical cutoff walls to restrain the movement of groundwater at contaminated sites. However, the conventional cement-based slurry needs a long time to evolve satisfactory performance along with a relatively high environmental load. This paper proposes an innovative material for the self-hardening slurry system, consisting of reactive MgO, slag, bentonite and lots of water. The properties of fresh slurry, unconfined compressive strength (UCS) and permeability of the MgO activated slag and bentonite (MASB) slurry are investigated in comparison with SCB slurry. The results indicate that compared with SCB slurry, MASB slurry with appropriate proportions has comparative fresh properties, but possesses higher UCS and much lower hydraulic conductivity (close to 1.0 × 10−10 m/s) at a later age. A massive formation of expansive hydration products (hydrotalcite phases) could satisfactorily fill in the voids of matrix, leading to a dense microstructure which is responsible for the excellent mechanical and penetrative performance of MASB slurry. The overall findings from this study well demonstrate that the developed MASB slurry holds great potential as a novel, eco-friendly and cost-effective material in the construction of vertical cutoff walls.

Arsenic (As) is a naturally occurring trace element that may pose a threat to human health and the ecosystem, while effective remediation and sustainable reuse of As-containing soil is a challenge. This study investigated the geoenvironmental characteristics of a geogenic As-rich soil, and green binders (ground granulated blast slag (GGBS) and cement blends) were employed for the stabilization/solidification (S/S) of the soil under field-relevant conditions. Results indicate that the use of 10% binder could effectively immobilize As and chemical stabilization/physical encapsulation jointly determined the leaching characteristics of the S/S soils. The geogenic As could be effectively immobilized at the pH range of 5.5-6.5. The increasing use of GGBS enhanced the strength of the 28-d cured S/S soils because of long-term pozzolanic reaction, but also slightly improved the As leachability. Besides, the moisture content of the contaminated soils should be suitably adjusted to allow for desirable compaction of S/S soils, which resulted in high compressive strength and low of As leachability. Results show that soil moisture content of 20% was the most appropriate, which resulted in the highest strength and relatively lower As leaching. In summary, this study presents a sustainable S/S binder for recycling As-contaminated soil by using a combination of cement and GGBS.

To enhance the properties of recycled concrete aggregates (RCA), a liquid-solid carbonation process was developed and compared with the conventional gas-solid pressurized carbonation method. The performance of RCA and the recycled aggregate concrete (RAC) prepared with the carbonated RCA by the two aforementioned carbonation methods was evaluated. The carbonation products assemblage, microstructure and porosity evolution were first characterized. The results indicated that after subjecting to a 10-min liquid-solid carbonation process, a reduction of 12.2% in RCA water absorption and an increase of 2.6% in density were achieved, which were more efficient when compared to the 24-h gas-solid pressurized carbonation. More importantly, the compressive strength of RAC prepared with the 6-h liquid-solid carbonated RCA was significantly improved. In light of microstructural analysis, the enhanced performance of RAC was attributed to more additional mono-carbonate (Mc) and C–S–H gel formed at the interface between the liquid-solid carbonated RCA and the new cement pastes.

The use of 100% waste glass cullet (WGC) as fine aggregates in architectural cement-based mortar had been proven to be feasible in previous works. This paper reports a further study on investigating the influence of using waste glass powder (WGP) as a supplementary cementitious material on the properties of glass-based architectural cement mortars. The experimental results showed a good linear relationship between the particle size of WGP and the flow values of the fresh mortar, revealing that the particle size of WGP played an important role in controlling the workability. For the hydration of white cement, the inclusion of WGP not only affected the second exothermic peak of hydration but also changed the third peak. In particular, the result indicated that the use of finer WGP had an advantage in increasing the flexural strength of the cement mortar when compared with the corresponding compressive strength, which was attributed to the morphological and pozzolanic effect of WGP. In addition, the very fine WGP could act as micro-fibers and micro-aggregates in filling the microstructure of the mortar. At 90 days of curing, the mortar prepared with finer WGP showed a distinct improvement in strength due to the improved interfacial transition zone and the pore-size refinement.

This paper presents an experimental investigation on the water resistance of magnesium oxychloride cement (MOC) incorporating incinerated sewage sludge ash (ISSA). Cement pastes were prepared to evaluate the compressive strength and microstructure of the blended cements. Besides, the volume stability of cement mixture during air curing and water immersion was tested by measuring the length change of mortar bar specimens. In addition to cement paste and mortar, Na2SiO3·9H2O and Al(NO3)3·9H2O were used to react with MOC as the replacement of ISSA to synthesize pure hydration products. Paste studies revealed that ISSA additions of 10–30% significantly improve the water resistance of MOC. Mortar studies showed that ISSA significantly reduced expansion of mortar bars immersed in water. The improved water resistance and reduced expansion is directly related to the decrease in MgO content of pastes and an improved stability of Phase 3 (3Mg(OH)2·MgCl2·8H2O) and Phase 5 (5Mg(OH)2·MgCl2·8H2O) in water. Results from sol-gel experiments suggest that ISSA can act as a source of soluble Al and Si which results in the formation of an amorphous M-Cl-A-S-H type cementitious gel. The gel formed could help improve Phase 3 and Phase 5 stability in water by interlocking mechanisms which impede the access of water to Phase 3 and Phase 5.