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Steel corrosion is one of the main factors limiting the durability of existing reinforced concrete components. Based on the corrosive circumstances, different prevention and repair methods can be applied. In the case of carbonation-initiated corrosion, chemical re-alkalisation (CRA) is one of the standard measures to counteract alteration processes in the concrete that lead to reinforcement corrosion. The current state of research on the CRA of carbonated concrete and the various materials that have been investigated in terms of their applicability for this repair measure are summarised. The review summarises current research results in the field of carbonated concrete and the proven pozzolanic reactivity of the carbonation products in contact with portlandite, which suggests an inhibitory effect on CRA, although this has not yet been investigated. There are also initial attempts that deviate from the application of classic Portland cement as a repair material, but their applicability in practice must be questioned. The use of alternative binders and the associated different compositions of pore solutions and varying alkalinity of these binders (e.g. composite cements with a high substitution rate or alkali-activated binders), have not yet been investigated for repair processes such as CRA, although the chemical composition of binders is of the greatest importance for successful application of the repair measure. [ABSTRACT FROM AUTHOR]

Alkali-activated materials (AAMs) are regarded as a substitute for Portland cement. They have high chloride resistance and a low carbon dioxide footprint. The aim of this review is to provide a multi-scale perspective to understand material–product–microstructure–property relationships in terms of the chloride binding behaviour of AAMs. The physical and chemical chloride stability of different reaction products is summarised from nanostructure, to microstructure to macro properties. An analysis of studies in the literature gives an overview of recent progress in chloride transport in AAMs influenced by different reaction products. Results show that a higher calcium/silicon, aluminium/silicon molar ratios and alkali content increase the formation of amorphous phases, leading to a denser microstructure and lower chloride penetration in AAMs. Higher magnesium oxide and aluminium oxide contents result in increased formation of hydrotalcite. The enhanced physical and chemical absorption of chloride by hydrotalcite leads to higher resistance of chloride penetration in AAMs. Investigation of increasing chloride resistance could potentially focus on increasing gel and hydrotalcite formation. [ABSTRACT FROM AUTHOR]

Although alkali-activated materials (AAMs) are considered potential substitutes for Portland cement, they still come with elevated costs and significant carbon dioxide emissions. The development of alternative activators, such as sodium silicate based on the dissolution of rice husk ash (RHA), could partially overcome these disadvantages. However, to maximise the mechanical performance of AAMs, the production of RHA-based sodium silicate (RHA-SS) needs to be fully understood. The production process of an alternative RHA-SS activator was thus investigated through experimental evaluations of RHA grinding time, RHA dissolution time and thermal curing temperature and time. Mechanical performance was evaluated through compressive strength tests carried out on alkali-activated pastes made up of metakaolin, as a precursor, and two different activators (RHA-SS and a commercial sodium silicate). Microstructural features were evaluated through X-ray diffraction, scanning electron microscopy and thermogravimetry analyses. Optimal production was obtained for a grinding time of 30 min, a thermal curing temperature of 40°C, dissolution time of 6 h and a thermal curing time of 8 h. The results show the efficiency of the alternative alkaline activator, which may represent a technically viable solution for larger scale application to AAMs. [ABSTRACT FROM AUTHOR]

Steel slag (SS) is a by-product of the steel industry, and its recycling is of great significance. In this study, the influence of SS fineness and curing regimes on the hydration properties of cement and the effects of SS content on the compressive strength of pastes were investigated. The hydration products and microstructure of pastes were further explored through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the compressive strength decreases gradually with the increase of SS, and increases with the increase of the specific surface area of SS. The compressive strength of paste after steam curing is improved, and the compressive strength of the paste mixed with 30% SS can reach more than 50 MPa after 90 days of steam curing. The hydration products of paste mixed with SS are not significantly different from those of cement, which mainly comprise calcium hydroxide (Ca(OH)2) and calcium silicate hydrate (C–S–H) gel, accompanied by a small amount of calcium carbonate (CaCO3). SS has secondary hydration after long-term ageing and can fill and refine the pore structure, according to SEM. Using SS as a supplementary material is beneficial in terms of reducing cement cost and lowering carbon dioxide (CO2) emission. [ABSTRACT FROM AUTHOR]

On the one hand, calcium sulfoaluminate (CSA) eco-cements release about 40% less carbon dioxide (CO2) than Portland cement during fabrication; on the other hand, phase change materials dispersed in a cementitious matrix can help to optimise the indoor temperature of buildings, reducing carbon dioxide emissions related to heating/air conditioning. However, this is only economically viable if it is used as a thin layer (a coating). In addition, the combination of both materials supposes a double environmental benefit. Consequently, the main objective of this work is the preparation of a suitable homogeneous and well-adhered bilayer sample, composed of CSA and CSA-MPCM. To achieve this, in the first step, the effect of pH, temperature and stirring was studied for microencapsulated phase change material (MPCM) aqueous suspensions (47.3 wt%); second, the MPCM (45 wt% with respect to dry cement) was dispersed in a CSA paste; then, in a third step, a homogeneous well-adhered coating of CSA-MPCM, with undamaged MPCM, was obtained on a CSA matrix. This was achieved through rheological measurements and checked by microscopy. Finally, the corresponding CSA and CSA-MPCM mortars were characterised through their mechanical properties (compression) (70 and 13 MPa at 7 days, respectively) and thermal conductivity (2.06 and 1.19 W/mK, respectively). [ABSTRACT FROM AUTHOR]

The AFm phase found in hydrated Portland cements refers to a family of calcium aluminate phases. Their layer structure is derived from that of portlandite (calcium hydroxide (Ca(OH)2)), but with one third of the Ca2+ ions replaced by a trivalent ion, nominally Al3+ or Fe3+. The resulting charge imbalance gives the layers a positive charge, which is compensated by intercalated anions; the remaining interlayer space is filled with water (H2O). Hydrated cements will contain mixtures of AFm phases and their solid solutions. Portland cement is often modified by addition of soluble nitrate or nitrite salts to protect embedded steel or to shorten the setting time. These nitrate and nitrite ions are capable of entering and occupying AFm anion sites, hence impacting overall phase balances between cement hydrates. In this study AFm phases and solid solution formations were investigated between AFm phases containing SO42−, CO32−, OH−, Cl− and NO2− NO3− ions. Samples were synthesised and subsequently characterised using X-ray diffraction and through the measurement of aqueous solution compositions after 180 days of equilibration in water. [ABSTRACT FROM AUTHOR]

The aim of this work was to conduct a rheological assessment of mortars based on the automated slump test. Using this test to monitor the transient and permanent regime of slump and its spread, the parameters were correlated with the rheological properties of the mortars. Based on dimensionless slump/spread, yield stress and viscosity, empirical models were developed for obtaining rheological parameters, which provided correlations with good coefficients of determination (R2 > 0.85). Through analysis of the slump behaviour of the mortars, a correlation between the viscosity and the maximum slump velocity was obtained (R2 = 0.90), showing that viscosity could be determined based on the slump velocity. Furthermore, based on a physical description of the slump test related to the Reynolds number, three distinct stages in the slump process were defined: the viscous phase (characterised by high viscosities), the intermediate phase (the coexistence of viscous and inertial effects) and the inertial phase (characterised by low viscosities and a higher sensitivity to lifting of the mould). The dynamic similarity of the analysed mortars (vertical Reynolds number/radial Reynolds approximately equal to one) indicated that the shear rate could be measured based on the vertical direction of the flow (slump). [ABSTRACT FROM AUTHOR]

This study uses conventional 87Sr/86Sr and 143Nd/144Nd isotope and interelement ratios of Ca, Sr, K, Mn, Mg and Ti as fingerprints for provenancing ordinary Portland cements (OPC). Herein, the first database of Sr and Nd isotope ratios investigated in OPCs, stemming from 29 cement plants located worldwide, was created. The results show that the Sr isotope ratios of OPCs are higher than those of seawater from the observed geological period. The spread of 143Nd/144Nd in OPCs is not as large as the spread for 87Sr/86Sr isotope ratios. However, the combination of both Sr and Nd isotope ratios provides the potential for distinguishing between cements of different production sites. Most of the OPCs investigated have measurable differences in their 87Sr/86Sr and 143Nd/144Nd isotope ratios, which can be employed as a valuable analytical fingerprinting tool. In the case of equivocal results, divisive hierarchical clustering was employed to help overcome this issue. The construction of geochemical profiles allowed the computing of suitably defined distances between cements and clustering them according to their chemical similarity. By applying this methodology, successful fingerprinting was achieved in 27 out of the 29 ordinary Portland cements that were analysed. [ABSTRACT FROM AUTHOR]

A study was undertaken to evaluate the embodied greenhouse gas emissions of four different design options for the foundation of a residential modular building in the East Midlands, UK. The assessment considered the embodied carbon dioxide equivalent of material production (without and with Portland cement replacement using ground granulated blast-furnace slag), transportation, construction works (such as soil excavation) and plant usage on site and off site. The findings indicated that helical piles and reinforced concrete slabs supported with expanded polystyrene were the most sustainable options (in terms of embodied emissions) compared with conventional strip and pad foundations. This study provides valuable insight into considerations and constraints that may arise when evaluating the sustainability of modular building foundations. It offers practical guidance for decision makers in the modular construction sector seeking to mitigate the environmental impact of their geotechnical design. [ABSTRACT FROM AUTHOR]

Belite sulfoaluminate cement is attracting increasing attention and being considered as a potential alternative to ordinary Portland cement owing to lower preparation temperature and carbon dioxide (CO2) emission. However, it still has disadvantages of poor workability and low early strength. This study investigated the effects of compound polycarboxylate superplasticiser (PCE) and early strength agent, calcium nitrite (Ca(NO2)2), on flowability and early strength of belite calcium sulfoaluminate (BCSA) cement. Variation patterns of setting time, fluidity, strength and polycarboxylate superplasticiser (PCE) adsorption of the paste were measured; the hydration products and microscopic morphology were also analysed by the heat of hydration, X-ray diffraction and scanning electron microscopy. Results showed that calcium nitrite effectively enhanced adsorption of PCE onto the surface of BCSA cement particles, leading to notable improvement in the fluidity of the paste (reaching up to 275 mm). In the initial hydration stage, 0.7% PCE compounded with 1.2% calcium nitrite inhibited the formation of ettringite (AFt), resulting in prolonged setting time. However, it deepened the degree of hydration of BCSA for 3 days and refined the hydration product, AFt crystals. Consequently, the compressive strength was increased to 95.75 MPa and 107.13 MPa for BCSA cement at 3 days and 28 days, respectively. [ABSTRACT FROM AUTHOR]

Concrete technologists use different types of additives such as fly ash, slag, natural pozzolans and nanomaterials toenhance concrete performance and durability. However, a detailed explanation of the early-age hydration process and microstructural modification of concrete in the presence of nanomaterials remains to be presented and extensive research is required for strategic modification of cementitious systems. This study focused on the precise monitoring of early-age hydration with the incorporation of nanoalumina (nAl) in tricalcium silicate (C3S) and Portland cement paste and mortar. The dosage of nAl was varied from 1 to 5% (by weight) in C3S and from 0.1 to 1.0% in Portland cement, with a water/cement ratio of 0.4. The hydration studies showed that the nAl increased the cross-linkage in calcium silicate hydrate gel through substitution of aluminium by silicon, which was responsible for the enhancement of the modulus of elasticity (by 40%) with 1.0% nAl) after 7 days of hydration. In summary, the incorporation of nAl modified the concrete microstructure in the initial days of hydration, leading to higher concrete performance and longer service lives of concrete structures. [ABSTRACT FROM AUTHOR]

Belitic calcium sulfoaluminate (BCSA) cement has well-established advantages such as a fast setting time, fast strength gain, long-term strength, shrinkage and sustainability. BCSA cement reaches an initial set in about 15 min at room temperature and can reach compressive strengths of over 27 MPa in about 2 h. While it can be mixed in a similar fashion to Portland cement (PC), a set retarder (such as citric acid) is usually required to achieve adequate working time and the design of mixtures differs slightly from PC designs. This paper provides guidance on establishing mix design criteria for BCSA cement. Slump and compressive strength studies measurements were taken for varying mixture proportions with strengths measured up to 1 year of hydration. For BCSA concrete mixtures, a relationship between water content and slump was established. Citric acid was found to increase the slump, especially at lower water contents. A relationship between setting time and citric acid dosage was proposed on the basis of mortar penetrometer and Vicat needle tests. X-ray diffraction analysis was also conducted on BCSA cement pastes with different water/cement (w/c) ratios. Crystalline structure growth was found to be directly related to the w/c ratio and inversely proportional to compressive strength. [ABSTRACT FROM AUTHOR]

The ultrasonic pitch–catch method was used to study the hydration behaviour of Portland cement paste with sodium gluconate (SG) additive using a tailor-made piezoelectric transducer. X-ray diffraction analysis showed that the intensity of the diffraction peak of calcium hydroxide decreased with increasing SG content (CSG), especially for CSG > 0.10 wt%. The compressive strength of the hardening cement pastes decreased remarkably for the pastes with CSG > 0.05 wt%. Ultrasonic waveforms appeared after 2 h of hydration and the waveform amplitudes of cement pastes with SG contents of 0.15 wt% and 0.20 wt% were obviously larger than those of cement pastes with CSG = 0.05 wt% in the early hydration stage. The hydration process of the cement paste over 300 h was classified into three stages based on the head wave amplitude variation – the fluctuation period, the rapidly increasing period and the smoothly increasing period. The acoustic propagation time changed greatly with hydration before a hydration age of 48 h, indicating that the hydration and hardening process of the cement paste was intense in the first 48 h. The proposed ultrasonic monitoring method opens a new perspective for studying the hydration behaviour of SG-blended cement paste. [ABSTRACT FROM AUTHOR]

Fused cement clinker can be produced from molten basic oxygen furnace slag (BOFS) by way of a reductive thermochemical treatment. During the thermochemical treatment, oxidic iron is reduced to metallic iron and separated. The resulting low-iron slag has a chemical and mineralogical composition similar to ordinary Portland cement (OPC) clinker. In this study, the hydraulic reactivity of the fused clinker from BOFS with and without gypsum was investigated using isothermal calorimetry, differential scanning calorimetry, in situ X-ray diffraction and powder X-ray diffraction. Furthermore, a synthetic fused clinker without foreign ions and fused clinker produced by a mixture of both materials was studied. The hydraulic reaction of the fused clinker from BOFS was considerably slower than that of OPC. However, the reaction can be accelerated by adding gypsum as a sulfate carrier. Furthermore, the results showed an increased reaction rate with decreasing content of foreign ions such as Fe, P or Mn. [ABSTRACT FROM AUTHOR]

Construction and demolition waste (CDW) management and recycling practices are crucial for transitioning to a circular economy. The focus of this study was on the detailed characterisation of different CDWs (hollow brick (HB), red clay brick (RCB), roof tile (RT), concrete and glass) collected from seven different demolition sites in Turkey. The CDWs were characterised based on particle size distribution, chemical composition and crystalline nature. Pozzolanic activity was evaluated through compressive strength measurements of cement mortars made with 20% cement replacement by CDWs at 7, 28 and 90 days. The results showed that the clayey CDWs exhibited similar physical/chemical properties and crystalline structures. The compositions of the waste concretes varied significantly based on their original materials. All the CDWs satisfied the minimum strength activity index (SAI) for supplementary cementitious materials, with pozzolanic activity influenced by the fineness and silica + alumina contents. The average SAIs for the HB, RCB, RT, concrete and glass were, respectively, 84.5%, 86.3%, 83.4%, 80.7% and 75.8%. Clayey CDWs contributed to mechanical strength development, while the contribution of concretes was related to the hydration of unreacted cementitious particles. Glass exhibited the weakest pozzolanic activity due to its coarser particle size. Overall, the CDWs demonstrated suitable properties for use as supplementary cementitious materials in Portland cement based systems. [ABSTRACT FROM AUTHOR]

Carbon dioxide sequestration in cement-based materials has emerged as a promising avenue for utilising captured carbon dioxide (CO2) and reducing the carbon dioxide footprint of the concrete industry. This article presents a comprehensive review of various studies conducted in this domain with a particular emphasis on factors affecting the carbon dioxide uptake potential of various concrete types and the effect of carbonation on the critical properties of concretes. Studies conducted on the micro-mechanical analysis of carbon sequestered concrete show that carbonation significantly improved the microhardness of the concrete samples, thereby increasing the strength and reducing the cement intake requirement. Further, keeping two parameters, namely water/solid (w/s) ratio and carbonation reaction time, in focus, the carbon dioxide uptake capacity in concrete slurry waste (CSW) was evaluated using non-linear regression analysis. It was observed that CSW paste had a maximum carbon dioxide uptake with an intermediate w/s ratio of 0.2 due to carbon dioxide reaction hindrances during diffusion at a higher w/s ratio and lack of hydration at a lower w/s ratio. On the contrary, for belite-rich cement, a higher w/s ratio led to higher carbon dioxide uptake owing to belite phase consumption leading to increased calcite production. Additionally, comparing the maximum carbon dioxide uptake capacity of CSW at a particular condition with various other cement-based materials, it was observed that belite-rich cement had the ability to sequester the maximum amount of carbon dioxide compared to the other cement-based materials considered in this study. [ABSTRACT FROM AUTHOR]

The Kosciuszko Bridge carries a 1.8 km long segment of the Brooklyn–Queens Expressway over Newtown Creek between Brooklyn and Queens in New York City, USA. The roadway is a vital link in the region's transportation network, carrying over 170 000 vehicles/day. Owing to structural and operational deficiencies, the existing structure was replaced. The new bridge consists of two parallel structures, one eastbound and one westbound, with main spans mirroring one another. Each structure consists of a single-tower cable-stayed main span over Newtown Creek with unbalanced main and back spans. This was the first cable-stayed bridge to be constructed in New York City, joining the ranks of the city's most iconic bridges. Here, two main span structures are discussed, with the focus primarily on the design and construction of the westbound, phase 2 bridge. Some key design aspects are outlined, including outboard cable anchorages, a concrete-filled counterweight and other details intended to facilitate construction, maintenance and inspection. The eastbound, phase 1 bridge was constructed under a design–build contract, and the westbound, phase 2 bridge as a design–bid–build. The paper also touches on some of the design aspects that were refined during the second phase. [ABSTRACT FROM AUTHOR]

According to what is extensively and logically assumed, a better anti-thixotropic behaviour than thixotropy was expected for shear-thickening cement pastes. However, the shear-thickening Portland and volcanic cement pastes studied here showed apparent thixotropic behaviour when step-up tests were performed. This unexpected result was tentatively justified assuming that, just at the beginning of the step-stress, virtually instantaneous particle aggregation (for step-up tests) and disaggregation (for step-down tests) take place. In other words, the existence of fast jamming or unblocking mechanisms developed by shear-thickening cement pastes was hypothesised. Then, it was supposed that the initial reorganisation of cement particles was followed by a progressive erosion of the jammed state (step-up) or progressive aggregation of the unblocking state (step-down) due to the constant action of shear stress. These ideas were used to model an empirical equation for the dependence of viscosity on shear stress, which can be used for cement applications. [ABSTRACT FROM AUTHOR]

Cement hydration has a direct influence on the mechanical and durability properties of concrete. Understanding the formation and evolution of hydration products at atomic scale during different stages of hydration is important in order to engineer the material for specific performance. However, research investigations on the effects of adding supplementary materials like fly ash (FA) on the development of the atomic scale structure of the major hydration product, calcium silicate hydrate (C–S–H), and its correlations with nanomechanical properties (through complementary physicochemical and nanomechanical techniques) are scanty. In this work, FA was added to Portland cement in different percentages (20% and 40%) to study its effect on the structural and mechanical properties at different phases of hydration (3–90 days). The evolution of C–S–H at atomic scale in cement–FA systems was studied using X-ray diffraction, atomic pair distribution function, high-resolution transmission electron microscopy, field emission scanning electron microscopy and Fourier-transform infrared spectroscopy, and mechanical properties at different ages were evaluated using a nanoindentation technique. The information and critical observations from this study provide significant information on intrinsic properties of hydrating cement composites, which will help in developing low-energy cement composites for sustainable structures. [ABSTRACT FROM AUTHOR]

Troublesome events are related to the stabilisation of sulfate-rich soils with calcium-based materials. To overcome these inconveniences, research studies have been conducted applying modified and alternative treatments to soils containing low and high sulfate levels. This paper intends to assess the effects of mellowing period (MP) (2 and 4 days), Portland cement content (5%, 7% and 9%), density (15.75, 16.60 and 17.50 kN/m3) and curing time (14 and 28 days) on the performance of a clayey soil from the Paraguayan Chaco region containing high amounts of sulfates. A complete factorial design set was carried out to assess the unconfined compressive strength (UCS) and the one-dimensional free vertical swelling of compacted soil–cement–lime mixtures. The results showed a positive effect of the MP relative to the swelling of the stabilised soil. In addition, the curing period, the amount of cement and the dry unit weight were the most influential factors regarding the UCS. The stabilisation method addressed in this research – that is, extended mellowing combined with lime and Portland cement, seems to be of great importance for practical purposes on the stabilisation of soils containing high amounts of sulfates. [ABSTRACT FROM AUTHOR]

The effects of nano-silica (NS) and nano-alumina (NA) additions on problematic marl soil in Tabriz, Iran were investigated. Marl soils constitute the foundations for most projects in Tabriz. Due to water absorption, these soils are liable to volume change, leading to instability risks in the foundations. Various physical and chemical methods have been employed to stabilise these soils. In the present study, for the first time, reconstructed samples of Tabriz marl were stabilised with various percentages of NS and NA, which have fewer negative environmental effects compared with ordinary additives such as Portland cement or lime. Soil swelling behaviours were evaluated experimentally using tests for Atterberg limits, density, free swelling, swelling pressure, California bearing ratio (CBR) and direct shear. Field emission scanning electron microscopy and X-ray powder diffraction analyses were conducted at curing times of 1, 7 and 28 days. It was found that NA had a greater effect on reducing the swelling of stabilised samples than NS. However, NS had a greater effect on increasing the strength (CBR). [ABSTRACT FROM AUTHOR]

The shrinkage and internal relative humidity (RH) of internally cured high-strength engineered cementitious composites (HSECCs) based on ordinary Portland cement (OPC) were experimentally investigated. Natural zeolite and calcined zeolite particles were used as internal curing agents. The effect of calcination and substitution ratio of zeolite on the shrinkage reduction efficiency and the compressive strength of the composites was evaluated. The test results showed that the development of shrinkage and internal RH of the OPC-HSECCs followed a two-stage pattern. Regarding shrinkage reduction of the OPC-HSECCs, the efficiency of the pre-wetted calcined zeolite particles was greater than that of the natural zeolite; the total shrinkage was reduced by more than 54% at 28 days and the compressive strength was similar to the control. The optimum replacement ratio of calcined zeolite was determined to be around 30%. [ABSTRACT FROM AUTHOR]

To solve the environmental problem of iron tailings, the preparation of green binding materials using iron tailings powder (ITP) shows bright prospects. However, the low activity of ITP limits its use as supplementary cementitious materials in large amounts. In this work, the activity of ITP treated for different milling times and at different sintering temperatures was studied, as well as the effects on the properties and microstructure of blended cement. It was found that ITP has a filling effect and provides additional nucleation sites. Additionally, ITP exhibits pozzolanic activity and consumes more hydration products at the later stage, which promotes the formation and deposition of C-S-H. All of these factors are related to the specific surface area (SSA) of the ITP and provide the conditions for cement paste densification, laying a foundation for the strength of cement blended with ITP. In summary, the activity of activated ITP is related to its SSA. It takes a long time for ITP to show pozzolanic activity. Activated ITP undergoes a secondary reaction to form a hydration product. The environmental impact and cost of pure cement pastes were higher than those of the cement–ITP pastes. [ABSTRACT FROM AUTHOR]

Preventing the corrosion of cementitious materials in acidic environments is crucial for the safety and durability of infrastructure. The corrosion of specimens of ordinary Portland cement (OPC) and metakaolin-based geopolymer (MKG) in 1 mol/l nitric acid solution was investigated in this work. The changes in morphology, mass, compressive strength, pH, chemical composition, crystal phases and pores were compared and analysed. The surfaces of the OPC specimens were corroded into petaloid grooves due to the relatively severe reaction between the calcium hydrated products and the nitric acid solution. The increase in the porosity of the OPC specimens was greater than that of MKG specimens, whose main constituents reacted with the nitric acid solution relatively mildly. However, large quantities of fragments peeled away from the MKG specimens, and their mass and compressive strength losses were greater than those of the OPC specimens. The porosities of the MKG specimens were only slightly changed. The strength loss of the MKG specimens was mainly due to broken matrix structures and newly formed porous silicious frameworks. [ABSTRACT FROM AUTHOR]

Effective binders with low environmental impacts are of great importance for sustainable engineering practices. Parameters controlling loss of mass and stiffness degradation of 'green' stabilised bauxite tailings (BT) were evaluated. The porosity/binder index (η/Biv) was investigated. This index allows unification of all experiments in a single relation for a specimen's porosity and binder content, resulting in a rational dosage methodology for any soil–binder blend, replacing conventional (trial and error) strategies that are laborious and time consuming. Wetting–drying cycles (durability tests) and pulse velocity tests were performed. The alkali-activated binder was composed of sugarcane bagasse ash and carbide lime (precursors) and sodium hydroxide (alkaline activator). For comparison, BT were also stabilised with Portland cement. For both cementing agents, stiffer specimens were less susceptible to the abrasive action of durability cycles. Diverse stiffness behaviours were observed due to the different curing periods needed for the development of chemical reactions for each binder. η/Biv was found to be an appropriate parameter for evaluation of loss of mass and stiffness degradation: lower porosity and higher cement content resulted in better mechanical performance. Through η/Biv, engineers can choose the best option for a project by decreasing porosity (increasing soil compaction) and reducing the binder content or, inversely, increasing porosity while raising binder content. [ABSTRACT FROM AUTHOR]

The dielectric properties of cement concrete are not only related to the dielectric properties and volume ratio of each component, but also related to frequency and temperature. In order to analyse these influencing factors, a dielectric constant test was done in the laboratory. Experimental results show that the dielectric constants decrease linearly with increase of temperature and decreases exponentially with the increase of frequency. Based on the experimental rules, a new dielectric model including frequency and temperature is established and verified by experiments. The verification results show that the calculation accuracy of the comprehensive dielectric model after considering the influence of frequency and temperature is improved by 25.5%, which meets the requirements of engineering detection accuracy. The model is applied to engineering practice, and the calculation methods of pavement structural layer thickness and moisture content are developed. The results show that the comprehensive dielectric model established in this paper has smaller error and higher accuracy. Using this dielectric model, the data conversion between different frequency and temperature can be achieved. The research results of this paper can provide a reference and basis for the quality evaluation of concrete structures. [ABSTRACT FROM AUTHOR]

Low-reactivity fly ash (LRFA), obtained from combustion in a low-temperature furnace, is a hazardous waste with low pozzolanic activity that is unsuitable for engineering applications. This study investigated the effects of mixing procedure (sequence mixing method (SMM) and conventional mixing method (CMM)) on the properties of a geopolymer made from LRFA blended with calcined kaolinite clay as a precursor. A mixture of sodium hydroxide and sodium metasilicate was used as the alkaline solution. It was found that the SMM was required to obtain LRFA geopolymers with sufficient strength for engineering applications. Using the CMM, the geopolymer had high porosity and low strength because gas bubbles were generated in the reaction between the alkaline solution and impurities in the LRFA during the hardening process. By contrast, in the SMM, the generated gas bubbles were released before the geopolymer hardened. As a result, the porosity was reduced and the strength was thus significantly increased. The 7-day strength of the geopolymer fabricated using the SMM was higher than the minimum requirement for Portland cement. In addition, the SMM reduced the setting time of the LRFA geopolymer, which is advantageous for rapid repair applications. [ABSTRACT FROM AUTHOR]

Light-burnt dolomite (LBD) as a compound magnesium oxide (MgO) expansive agent can compensate for the shrinkage of concrete effectively at early ages. However, in terms of strength, the replacement amount of Portland cement with LBD is limited due to the low reactivity of calcite in LBD. In this study, metakaolin used as a modified material was incorporated into blended cements containing LBD to improve the reactivity of calcite in the LBD. The results showed that the incorporation of LBD and metakaolin decreased the hydration heat and strengths of Portland cement at early ages, but the strength increased with increasing the mass ratio of metakaolin to LBD at later ages. In particular, the strengths of the blended cement containing 20% metakaolin and 20% LBD were even higher than those of Portland cement. This was mainly related to the formation of a compact pore structure with decreased porosity owing to the improvement of the reactivity of calcite in LBD and the pozzolanic reactivity of metakaolin. In addition, in comparison to Portland cement, the incorporation of LBD and metakaolin could produce a certain expansion due to the high hydration reactivity of magnesium oxide in LBD, and mitigated the shrinkage. [ABSTRACT FROM AUTHOR]

During the process of oil and gas exploration and development, the cementing operation is the key factor to ensure oil well productivity, and the performance of additives is directly related to the success or failure of cementing. In this study, the polymer retarder PID-1 was synthesised by aqueous solution polymerisation; the chemical structure, thermal stability and microstructure of PID-1 were studied by infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. In addition, the retarding effect and mechanism of PID-1 were analysed based on low-field nuclear magnetic resonance analysis, adiabatic calorimetry and scanning electron microscopy. Then, the polymer/organic compound high-temperature retarder PID-2 was constructed by adding organic compound PN with well retarding property; the retarding effect, thickening property, temperature and dosage sensitivity of PID-2 were then investigated. Combined with porosity evolution, type and content of hydration products, the internal mechanism of retarder PID-2 in relation to early mechanical strength development of the cement slurry system was revealed. [ABSTRACT FROM AUTHOR]

The mutual inhibition effect of transport of sulfate and chloride in concrete specimens was determined in a macroscopic experiment. A higher concentration of sulfate has a better inhibition effect on chloride transport and the opposite is also true. In this paper, molecular dynamics (MD) simulation was performed to explore the effect of concentration (0, 0.5, 1.0 mol/l) on the transport of mixed solutions (sodium chloride (NaCl) and sodium sulfate (Na2SO4)) in the main hydration products of aluminium-doped cement-based materials (i.e. calcium–aluminium–silicate–hydrate (C–A–S–H) gel). Sulfate was found to promote the aggregation of other ions to form ion clusters, which can reduce the effective width of the channel entrance and create a 'necking' effect, thus reducing the overall transport rate of the solution. With the increase of sodium chloride concentration, sulfate ions in the mixed solution can adsorb more Na+ and Cl− ions, and then form larger ion clusters to block the nanopores. Moreover, with increasing sodium sulfate concentration, a higher amount of sulfate ions existing in the solution makes it possible to form more ion clusters. The results can provide a reasonable nanoscale explanation for macroscopic experiment. [ABSTRACT FROM AUTHOR]

Finding alumina carriers that can replace bauxite to produce sulfoaluminate cement (SAC) is a significant issue. The effects of bauxite (Ba), industrial aluminium hydroxide (I-AH), industrial aluminium oxide (I-AO) and analytically pure aluminium oxide (A-AO) on the phase formation and mechanical properties of SAC clinkers were studied by differential scanning calorimetry/thermogravimetry, Rietveld quantitative analysis, scanning electron microscopy/energy dispersive spectrometry and isothermal calorimetry. It was found that sintering SAC clinker with Ba and I-AH as alumina carriers accelerated the rate of the solid-phase reaction, promoted the formation of the target phase and led to the formation of ye'elimite with a small grain size. The compressive strength at each age was thus higher. However, when amorphous alumina was used as the alumina carrier to sinter SAC clinker, the solid-phase reaction rate was slow, which hindered the formation of the target phase, free alumina appeared and ye'elimite with a large grain size was formed, so the compressive strength at each age is lower. Aluminium oxide with finer particle size can be decomposed from I-AH and Ba during calcination, which can accelerate the solid-phase reaction rate and promote the formation of the target phase. The associated element in Ba (titanium) can lead to the formation of more α′H-C2S, but obstructed the formation of ye'elimite. [ABSTRACT FROM AUTHOR]

The effect of temperature (10°C, 27°C and 50°C) on the hydration kinetics, phase assemblages and strength development of calcined clay blends (CCBs) was investigated at two replacement levels. The temperature sensitivity of the CCBs significantly increased when clinker was replaced with calcined clay, even at a 30% replacement level. The compressive strength development of the CCBs was higher than that of ordinary Portland cement at a lower temperature, perhaps due to the formation of low-density products such as stratlingite rather than enhanced clinker hydration. The reduced compressive strength development of the CCBs cured at 50°C could be due to multiple reasons (e.g. lower clinker hydration, reduced pozzolanic reaction, reduced stability of carboaluminates and ettringite). However, merely a 24-h lag in temperature exposure reversed this temperature effect, mainly due to the enhanced stability of carboaluminate and ettringite phases. The reduction in hydration was mainly in the belite phase and could be due to large changes in calcium alumina silicate hydrate having a high alumina substitution. It is hypothesised that the adverse effect of high-temperature exposure on CCBs is due to the formation of a physical barrier of highly polymerised calcium silicate hydrate on the surface of unhydrated clinker. The improved performance due to the delay in high-temperature exposure could be due to the enhanced stability of ettringite and carboaluminate phases. [ABSTRACT FROM AUTHOR]

Alternating current impedance spectroscopy (ACIS) was used to assess the effect of different sand, anhydrite and water contents on the electrochemical response of Portland cement paste in the early stages of hydration. Potential factors that may affect impedance measurements and data interpretation are also discussed, such as the complexity of the chemical composition of cement, its physical properties and hydration kinetics, and technique limitations. The impedance data obtained were benchmarked against different supporting techniques and literature data, showing a strong relationship among hydration rates as determined by thermochemistry, setting time measurements by physical approaches, pore fluid chemistry, electrical conductivity and the observed impedance behaviour. The results demonstrate that ACIS is a sensitive technique for assessing cement paste hydration, enabling differentiation of changes in the water and cement content, hydration degree and microstructural development during the first 24 h after mixing. [ABSTRACT FROM AUTHOR]

Accurate modelling of transient creep strain (TRC) is crucial for reliable fire performance assessments of concrete structures, since it is the largest strain component for structural concrete subjected to thermal exposure. Nonetheless, the mechanism underlying TRC is still not fully understood and most of the available models were established based on ordinary Portland cement concrete. As the most widely used supplemental cementitious material, the effect of fly ash on the development of TRC still requires further study. For this paper, steady state tests and transient state tests were carried out on ordinary Portland cement concrete (CEM I 52.5 as per BS EN 197-1, water/cement = 0.5) and fly ash concrete (class F fly ash as per BS EN 450-1, 25% replacement percentage), respectively. It was found that replacing 25% ordinary Portland cement with class F fly ash in concrete can mitigate the development of TRC above 400°C. Based on the experimental results, one assumption of the influence mechanism of class F fly ash on TRC is made and a TRC model for fly ash concrete (class F, 25% replacement percentage) at elevated temperatures is proposed. [ABSTRACT FROM AUTHOR]

In order to provide theoretical guidance for sulfoaluminate cement as grouting material used for coal mines, the purpose of this paper is to trace the hydration process and study the hydration kinetics of sulfoaluminate cement. The influence of the water/cement ratio (W/C) on the hydration exothermic characteristics of sulfoaluminate cement was studied by TAM air hydration microcalorimeter, Raman spectrum and compressive strength test, respectively. The results show that the rapid hydration of sulfoaluminate cement can be divided into three hydration processes: acceleration period, deceleration period and stability period. With the increase of W/C, the maximum heat release rate of cement decreases, while the cumulative heat release increases. In addition, increasing W/C can affect the microstructure of the cement paste, increase the porosity and further decrease the strength. Meanwhile, the Krstulović–Dabić model was used to analyse the hydration kinetics of sulfoaluminate cement with different W/C. The results show that the hydration mechanism of sulfoaluminate cement is not affected by increasing W/C. The hydration kinetics process can include three stages: nucleation and growth mechanism, phase boundary reaction and diffusion reaction. [ABSTRACT FROM AUTHOR]

Alkali-activated cements utilising fly ash can be a low-carbon alternative to Portland cement. However, fly ash alkali-activated cements require curing at elevated temperature and have cost plus environmental implications owing to the use of strong alkali solutions. Unclassified fly ash, silica fume, calcium hydroxide and sodium carbonate were used to develop novel one-part fly ash alkali-activated cements. When cured at ambient conditions, the cements gained compressive strength up to 11.0 and 44.2 MPa at 3 and 28 days, respectively. Microstructural investigations revealed that cation exchange reaction between the activators was the key element in the development of the microstructure and strength of the cements. The novel fly ash alkali-activated cements have at least 50% lower impact on global warming than highly blended Portland cements. [ABSTRACT FROM AUTHOR]

Wet stored fly ash is increasingly being considered as a cement component in concrete. However, the effect of these conditions on the material's reactivity is uncertain. The research described here investigated this property for wet laboratory-stored (10% moisture) and site stockpile fly ashes, using lime consumption (BS EN 196-5, Frattini) and activity index (BS EN 450-1) tests. Progressive reactivity losses occurred with laboratory storage up to 730 days. This was influenced by dry fly ash fineness and holding period, suggesting that the formation of agglomerates/products (assessed by scanning electron microscopy) affects lime's access to particle surfaces, with similar type behaviour for stockpile materials. Compressive (cube) strength reductions were also found between dry and wet stored fly ash concretes. Stockpile fly ash reactivity following laboratory- (drying/ball milling) and pilot-scale (flash drying/de-agglomerating, air classifying, micronising and carbon removal) processing was then investigated. Exposure of reactive material using these methods appears to be important, with greater improvements generally noted as the fly ash particle size is reduced and at later test ages. To meet activity index requirements, fly ash sub-10 μm contents, with the Portland cement used, needed to exceed about 30%, irrespective of the storage conditions/processing used. Minor benefits to concrete strength were obtained with increasing sub-10 μm contents, particularly beyond 28 days. [ABSTRACT FROM AUTHOR]

The objective of this study was to explore the influence of an alkali liquid accelerator based on sodium aluminate (ASa) on the early hydration behaviour of cement paste, tricalcium aluminate (C3A) and tricalcium silicate (C3S) and identify its accelerating mechanism. The setting times and mechanical properties of cement paste and mortar mixed with different amounts of ASa were determined. Isothermal calorimetry showed that the addition of ASa increased the first exothermic peak of cement hydration and advanced the second exothermic peak. The morphology of hydration products was analysed by scanning electron microscopy (SEM) and a model for the early hydration of cement paste was established. X-ray diffraction and SEM were also used to analyse the phase composition and morphology changes of C3A and C3S with or without ASa and early hydration models were established. Analysis of the experimental results revealed that the sodium hydroxide produced by ASa hydrolysis had the function of consuming gypsum, breaking calcium silicate hydrate gel film and increasing the calcium hydroxide concentration in the cement paste. The ettringite in the hydration products interweaved together to form a skeleton structure, which was conducive to cement paste hardening. [ABSTRACT FROM AUTHOR]

The effects of graphene oxide (GO) on the microstructure and resistance to chloride ion (Cl−) penetration of matrix containing 0-0.05% GO were investigated through isothermal calorimetry, thermogravimetric analysis, X-ray diffraction, mercury intrusion porosimetry and the rapid chloride penetration test method. A proper dosage of GO promoted the hydration process of cement, increased the calcium hydroxide (Ca(OH)2) content, refined the size of calcium hydroxide, promoted the formation of high-density calcium silicate hydrate and improved the pore size distribution of cement matrix. Compared to the group without GO, the porosity of concrete containing 0.03% GO decreased by 8.56%, the largest pore diameter decreased by 29.05% and pores larger than 50 nm were reduced by 36.93%. In addition, the incorporation of GO improved the resistance to chloride ion penetration of concrete. The charge passed through the concrete first decreased and then increased with the increasing GO dosage. When the dosage of GO was 0.03%, the charge passed through the concrete was 27.71% lower than that of the control group. There was a significant correlation between the permeability of chloride ions and pore structure, especially the proportion of pores larger than 50 nm of concrete. [ABSTRACT FROM AUTHOR]

Reuse of reclaimed asphalt pavement, RAP, provides an option to face the obstacles of both an economic and environmental nature, reintegrating the material into the soil as an alternative way either to dispose of it, or to reduce other aggregates' usage. However, total or partial substitution must be associated with an improvement technique to abide by norms and regulations requirements, such as cement stabilization and fiber reinforcement. The research presented in this paper aims to evaluate the effects of including 24-mm polypropylene randomly distributed fibers on a mixture of a cemented sandy soil with a substitution of 30% reclaimed asphalt pavement (RAP) in lieu of soil. The experimental program was developed to examine the mechanical behavior of the mixture, including unconfined compressive strength, flexural tensile strength, splitting tensile strength, pulse-velocity, durability, and monotonic and cyclic simple shear tests, over different mixture dosages containing 3%, 5%, 7% and 9% Portland cement, 0.5% fiber, over a compaction effort to achieve dry weights of 16.4 kN/m3, 17.2 kN/m3 and 18.0 kN/m3. The fiber reinforced mixtures were compared to literature results, utilizing the same materials. Results indicate improvement of strength and durability overall, and also a possible drawback concerning the material's Q3 shear modulus. [ABSTRACT FROM AUTHOR]

The mechanical and microstructural properties of alkali-activated slag cement (AASC) mixed with 2–10% zinc oxide (ZnO) were investigated. The addition of zinc oxide was found to be more effective for improving the strength at a later age: compared with AASC without zinc oxide, the addition of 10% zinc oxide improved the compressive strength by about 22% at 28 days. Furthermore, through the formation of zinc hydroxide (Zn(OH)2) and calcium zincate (CaZn2(OH)6.2H2O) and an increase in gel porosity (<10 nm), a dense matrix was formed, leading to an improvement in mechanical properties. At high pH, the ionisation of zinc oxide was promoted and the pH of the pore solution was increased. However, as the amount of zinc oxide was increased, unhydrated zinc oxide was observed between the hydration products. AASC has a higher alkali concentration than ordinary Portland cement, which improves the reactivity of zinc oxide and thereby improves strength by forming a high-density hydration product matrix. [ABSTRACT FROM AUTHOR]

This work investigates grinding as a potential solution to improve the utilisation of low-quality fly ashes in concrete. Factors contributing to the performance of ground fly ash in cementitious composites were investigated. It was found that grinding significantly crushed large cenosphere particles and increased the specific gravity and surface area of fly ash, which led to a higher filler effect and improved the rate of cement hydration, contributing to strength development. The comparison of strength of quartz-blended pastes and fly ash-blended pastes showed that the pozzolanic reaction of fly ash marginally contributes to strength development. The major influence of ground particles was seen in the region near aggregates. Ground fly ash significantly increased the microhardness of the interfacial transition zone near aggregates. Since this zone has a direct influence on the failure of mortars and concrete, its improvement resulted in a comparable strength of fly ash-blended mortars to the reference ordinary Portland cement mortar. [ABSTRACT FROM AUTHOR]

One-part geopolymers are a greener alternative to Portland cement and are more suitable in engineering applications compared with two-part geopolymers. The effects of mechanical activation on the properties and the mechanism of the pozzolanic reaction of fly ash (FA)/slag-based geopolymer paste prepared using the one-part method were studied. Simple mixing was used for the control group and the effect of mechanical activation on the macroscopic properties of geopolymers was studied using tests for compressive strength, fluidity and setting times. The effect of mechanical activation on the pozzolanic reaction of geopolymers was assessed using isothermal calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. The results showed that the 28-day compressive strength of the geopolymer formed by mechanical activation was 26% higher than that of the geopolymer prepared using simple mixing. Workability and fluidity were also enhanced. The reactivity of the precursor was improved by mechanical activation, particularly for the FA. The mechanically activated FA experienced a pozzolanic reaction within 7 days, while the undisturbed FA produced pozzolanic activity after 14–28 days. In addition, mechanical activation lessened the carbonisation of the one-part FA/slag-based geopolymer The implications of these results in terms of the influence of mechanical activation on pozzolanic activity are discussed. [ABSTRACT FROM AUTHOR]

Sulfobelite (belite-rich calcium sulfoaluminate (BCSA)) cements are promising alternatives to ordinary Portland cement (OPC) due to their lower carbon dioxide generation and lower energy consumption in the clinkering process. Additionally, they are cost effective because of their less-restrictive raw meal composition compared with that of calcium sulfoaluminate (CSA), in which expensive bauxites are used as the alumina source. Diverse mining residues have been proved to be reliable alumina sources for BCSA production, including the clay residues that cover bauxites (Belterra Clay (BTC)) in the Brazilian Amazon region. The clinkering settings of BCSA using a different (less alumina) BTC were examined in this work. The mineralogy of the BCSA clinkers was optimised by a design of experiments and studied using X-ray powder diffraction, scanning electron microscopy and thermal analysis. The raw meal composition, boron doping and firing temperature were investigated to obtain the optimal clinker composition. Hydration of the cement pastes was investigated by calorimetry and the strength development of mortars was tested and compared with that of a commercial OPC. The BCSA mortars produced with gypsum additions developed compressive strength comparable to that that OPC within 28 days. The main hydrated phase was ettringite, with minor amounts of kuzelite, straetlingite and gibbsite. [ABSTRACT FROM AUTHOR]

An experimental investigation was carried out on a novel type of concrete-filled tube column, which used geopolymer concrete and basalt-fibre-reinforced-polymer reinforcing bars and confinement tube. Geopolymer concrete was used in place of ordinary Portland cement concrete to counter the sustainability challenges of conventional cement manufacture. Longitudinal basalt-fibre-reinforced-polymer bars were used to replace steel reinforcement to avoid corrosion, while basalt-fibre-reinforced-polymer tube confinement was used to replace the conventionally used steel helix to enhance strength and ductility. Compressive load–deformation behaviour of 200 mm dia., 800 mm high specimens under concentric, 25 mm eccentric, 50 mm eccentric and four-point bending loads was experimentally investigated. Experimental axial load–bending moment diagrams were then produced. Although geopolymer concrete is normally considered to be more brittle than Portland cement concrete, the test results showed that the specimens with geopolymer concrete were more ductile compared to those with Portland cement concrete. It was also found that increased load eccentricity resulted in ductility enhancement in specimens with both types of concrete with basalt-fibre-reinforced-polymer bars and tubes, while steel-reinforced specimens suffered loss of ductility with increased load eccentricity. [ABSTRACT FROM AUTHOR]

The effects of limestone powder (LP) of different fineness on the packing density, strength and hydration behaviour of cement blended with a high volume of LP were studied using Vicat setting time tests, strength tests, isothermal calorimetry and scanning electron microscopy. Three different LP fineness values were examined and it was found that cement replacement by LP with the smallest median particle size produced the highest density. The compressive strength of the blended cement mortar increased with increasing LP fineness. The packing densities of the blended cement were used to infer the evolution of mechanical strength of the blended cement mortar. The addition of LP with a median particle size smaller than that of cement accelerated the hydration of cement in the acceleration period. Compared with LP with a median particle size smaller than that of cement, the production rate of nuclei of cement blended LP with a median particle size larger than that of cement decreased with increasing amounts of LP replacement, while the growth rate of nuclei increased with increasing amounts of LP replacement. [ABSTRACT FROM AUTHOR]

The phosphate mining industry produces large amounts of tailings. Rational utilisation of phosphorus tailings (PT) is of great significance for the full exploitation of waste resources and environmental protection. In this study, PT were used as one of the raw materials to prepare white Portland cement clinker (WPCC). Various techniques were used to study the effect of PT on the mineral composition, ionic solid solution and compressive strength of the WPCC. The results showed that using PT in WPCC significantly improved the burnability of the raw material, increased the liquid phase content and promoted the formation of minerals. The addition of PT was found to stabilise α′-C2S crystals and promoted the change of C3S crystals in the clinker from T-type to M-type. The addition of PT had no significant effect on the decomposition temperature of calcium carbonate, the appearance temperature of the liquid phase and the formation temperature of C3S. A PT content of 2.5% produced the highest strength of the WPCC: compared with the control group, the 3-day strength increased by 46.86% and the 28-day strength increased by 82.59%. [ABSTRACT FROM AUTHOR]

Limestone ternary cements (LTCs) have attracted significant research and commercial attention recently, for technical and environmental reasons. Standardisation of these cements is imminent under BS EN 197-5:2021. Detailed understanding of the hydration and microstructure evolution of LTCs from different alumina-rich supplementary cementitious materials exists in the scientific literature; improved reaction kinetics and additional phase assemblages refine the pore structure. However, understanding of the performance of LTCs under exposure conditions is less prevalent. In this contribution, the available data are reviewed in a way that allows stakeholders to appreciate the capabilities of the different compositions and their performance. The focus is a critical examination of the interplay between cement composition and microstructure and its effect on durability. It is demonstrated that LTCs offer a pathway for reducing the embodied carbon dioxide of concrete without compromising their performance. Resistance to chloride ingress, sulfate attack and alkali–silica reactions are significantly improved in a manner similar to binary cements. Compared with ordinary Portland cement, carbonation and freeze–thaw resistance are generally lower, but adequate air entrainment can offer an improvement in freeze–thaw resistance. The challenge to widespread adoption of LTCs is evidence of durability under field conditions. To this end, large-scale field trialling is recommended to gain understanding of the role of combined exposures on the durability and mechanical properties of LTCs. [ABSTRACT FROM AUTHOR]

Few studies have reported the effect of cement content and surcharge pressure on the drying−wetting durability of cement-stabilised clayey soil. The aim of this research was thus to understand the effect of these two factors on the drying−wetting durability of cement-stabilised clayey soil. Clayey soil, dredged from Taihu Lake in Wuxi, China, was stabilised with three different cement contents. Drying−wetting tests were performed on the cement-stabilised clayey soil under five different surcharge pressures and direct shear tests were conducted using a modified conventional direct shear device. The cement content was found to have a significant effect on the drying−wetting durability of the cement-stabilised clayey soil. Drying−wetting appears to decrease the shear strength of clayey soil with a low cement content, whereas drying−wetting appears to increase the shear strength of clayey soil with a high cement content. The variation in shear strength of the cement-stabilised clayey soil is attributed to drying-induced bond damage and drying-temperature-induced hydration and pozzolanic reactions. The surcharge pressure had a significant impact on the drying−wetting durability in a certain range. The findings are interesting from a practical perspective for earthworks involving cement-stabilised clayey soils. [ABSTRACT FROM AUTHOR]

The combined use of coal bottom ash (CBA) and ground CBA (GCBA) as partial replacement of fine natural aggregate (FNA) and Portland cement, respectively, was investigated for the production of concrete mixtures. Five concrete mixtures incorporating GCBA at 20 wt% replacement of binder and CBA at 0, 25, 50, 75 and 100 wt% replacement of FNA were produced and tested for strength, microstructural characteristics and carbonation resistance. A base concrete mixture made of conventional concrete was also produced as a reference concrete mixture. Test results showed that the combined use of GCBA and CBA in concrete mixtures results in enhancement of the microstructure, carbonation resistance and compressive strength of the resulting concrete mixtures. Scanning electron microscopy and X-ray diffraction analyses pointed at the occurrence of pozzolanic reaction and pore-filling effect of GCBA and CBA in the resulting concrete mixtures. It was observed that 25 wt% replacement of FNA with CBA is an optimum dosage considering its effects on the later age strength and durability characteristics of the resulting concrete mixtures. [ABSTRACT FROM AUTHOR]