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This paper deals with the optimization of reactive powder concrete mixtures with respect to the addition of silica fume and the type of polycarboxylate superplasticizer used. First, the properties of reactive powder concrete with eight different commercial polycarboxylate superplasticizers were tested in terms of workability, specific weight, and mechanical properties. It was found that different commercially available superplasticizers had significant effects on the slump flow, specific weight, and compressive and flexural strengths. The optimal superplasticizer (BASF ACE430) was selected for further experiments in order to evaluate the influences of silica fume and superplasticizer content on the same material properties. The results showed that the silica fume and superplasticizer content had considerable effects on the mini-cone slump flow value, specific weight, flexural and compressive strengths, and microstructure. There were clearly visible trends and local minima and maxima of the measured properties. The optimal reactive powder concrete mixture had a composition of 3.5–4.0% superplasticizer and 15–25% silica fume. [ABSTRACT FROM AUTHOR]

The current work highlights our capacity to accurately model a broad range of solidification/stabilization systems in order to select the best performing matrix as a function of the brine composition and concentration. [Display omitted] • The reactivity of 2 fly ashes is assessed as a function of the additive and the brine type. • Al- and Si-containing additives hinders the reactivity of the fly ashes. • Additives with no Al or Si content induce an increase in fly ash reactivity. • We propose a machine learning model that can predict the fly ash reactivity for accurate phase assemblage prediction. The pozzolanic reaction of fly ashes with calcium-based additives can be effectively used to solidify and chemically stabilize (S&S process) highly concentrated brines inside a cementitious matrix. However, complex interactions between the fly ash, the additive, and the brine typically affect the phases formed at equilibrium, and the resulting solid capacity to successfully encapsulate the brine and its contaminants. Here, the performances of two types of fly ash (a Class C and Class F fly ash) are assessed when combined with different additives (two types of cement, or lime with and without NaAlO 2), and two types of brine (NaCl or CaCl 2) over a range of concentrations (0 ≤ [Cl−] ≤ 2 M). The best performing matrices – i.e., the matrices with the highest Cl-containing phases content – were identified using XRD and TGA. The experimental results were then combined with thermodynamic modeling to dissociate the contribution of the fly ash from that of the additives. All results were implemented in a machine learning model that showed good accuracy at predicting the fly ash degree of reaction, allowing for the robust prediction of extended systems performance when combined with thermodynamic modeling. [ABSTRACT FROM AUTHOR]

Featured Application: We found that in the areas with high seasonal rainfall, to stabilize clay soils, if the amount of Montmorillonite mineral is greater than a certain amount (for example, in this study, 45%), with any amount of chemical additives, they do not maintain their stability and collapse. Conversely, soils containing certain amounts of Illite and Kaolinite minerals with the smallest amount of chemical additives have the best performance. Although the interaction between clay minerals and lime is the most effective factor in lime stabilization techniques, it has not been deeply evaluated. This research study investigated the microstructural characteristics of lime-stabilized Bentonite and Kaolin soils using X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray (EDX) analyses. To consider the variation in clay mineralogy, these soils were mixed at varied ratios, stabilized, and then subjected to a durability process. The microstructural findings showed that the pozzolanic reactions with lime did not occur or occurred at a low level for Bentonite soil. However, they occurred at a very high level for Kaolin soil. The durability test confirmed the microstructural results and showed that the samples in which Bentonite soil had a share of 40 to 100% by dry weight of the soil did not last with any percent of lime. When the Kaolin soil content reached 100% by dry weight of the soil, the specimens lasted in the best possible way, even with 4% of the lime. This study concluded that the determination of optimum lime content based on the amounts and types of soil clay minerals is an important innovation for geotechnical projects and may be very cost-effective. [ABSTRACT FROM AUTHOR]

Accelerated carbonation of cement mixtures consisting of class G cement, silica fume, metakaolin, or blast furnace slag was studied by thermogravimetric, X-ray diffraction and Fourier transform infrared analyses for 1 year. Surface parts were fully carbonated during the first 7 days. Polymerization of amorphous hydrates due to their decalcification was observed together with the rising amount of calcium carbonates and reformation of gypsum from ettringite and monosulfate. Decalcification of clinker phases took place fast after the depletion of portlandite. Although portlandite was still present in unblended pastes, because of slower carbonation rate in the surface parts and higher C/S ratio of amorphous hydrates, the carbonation front moved inward during 3 months. Pozzolanic reactions in the samples with 30 mass% of additives depleted portlandite, however, higher amounts of C–(A)–S–H phases with lower C/S ratio, denser microstructure and faster carbonation of surface parts ensured their resistance against carbonation throughout the monitored period. [ABSTRACT FROM AUTHOR]

The use of cement in construction is costly and degrades the environment. Therefore, affordable and easily available alternatives are needed. This study evaluated the effect of thermal treatment on the pozzolanic activity of clay soils. Three wetland clays collected from three sub-counties of Murang'a County, Kenya (Kahuro, Kiharu and Maragua Sub-Counties) were studied after thermal activation. Thermal treatment (calcination) was carried out in an electronic muffle furnace (Advantec KL-420) at 600, 700, and 800°C for a duration of 2 hours. The chemical oxide composition was evaluated using X-ray fluorescence (XRF). Three methods (electrical conductivity, Frattini test, and compressive strength test method) were used to assess the pozzolanic activity of clay. A decrease in the electrical conductivity of the lime-clay solution was observed over a 24 hour period. Results of the Frattini test showed that clay calcined at 600°C and 700°C reacted with Ordinary Portland Cement (OPC) - CEM-I and reduced CaO and OH- concentrations to levels below the solubility curve of Ca(OH)2. Calcination of clay from Kahuro and Maragua subcounties, at 600°C and 800°C, respectively, increased the strength activity index of cement blocks from less than 0.75 to about 1 after 28 days of curing. Therefore, a temperature range of 600-800°C was considered effective for calcination. We conclude that thermal treatment increases the pozzolanic activity of natural clay for use as a replacement for cement. Therefore use of blended cement may be a sustainable alternative to the use of cement alone. [ABSTRACT FROM AUTHOR]

Concrete is the most significant manmade substance in the world. Unfortunately, concrete has a significant carbon footprint since cement is produced so extensively. A sustainable substitute for cement is the use of fly ash, a byproduct of industrial waste. By evaluating the material's reinforcement bond characteristics, this study seeks to determine whether employing fly ash concrete for structural applications is feasible. The pull-out tests were conducted on specimens that had cement replaced with 0, 20, 25, and 30% fly ash, and the results were compared to those run on control specimens made of 100% Portland cement. The pull-out tests were performed on specimens using steel bars that were 12 mm, 20 mm, and 25 mm in diameter. Also, a compressive strength test was performed on specimens with 0, 20, 25, and 30 percent cement replaced with fly ash. As the fly ash percentage increases, the slump value decreases. This creates problems with the workability of the concrete because when the slump decreases, the strength of the concrete increases. In comparison to normal concrete specimens' tests performed with 100 percent ordinary Portland cement, the use of 25 and 30 percent cement replaced with fly ash enhances both the compressive and bond strength. [ABSTRACT FROM AUTHOR]

Using recycled brick powder (RBP) in blended cement is beneficial to energy saving and emission reduction. The hydration process of blended cement containing RBP is significant for the mechanical property and durability of concrete. The hydration mechanism of blended cement containing recycled brick powder (RBP) has been investigated through hydration heat, hydration degree, and hydration products of the pastes to reveal the effect of RBP on hydration and the reaction mechanism of RBP. The results show that the addition of RBP reduces the heat release during the hydration process, but its nucleation and dilution effects promote cement hydration. The inclusion of RBP also decreases the amount of Ca(OH)2 in the system. The content of the amorphous phase in the system continuously increases with hydration time, and after 28 days of hydration, the amorphous phase is derived from both cement hydration and the pozzolanic reaction of RBP. Between 28 and 90 days of hydration, the reactivity of RBP significantly increases. [ABSTRACT FROM AUTHOR]

To effectively utilize the effectively the solid waste-soda residue (SR) and fly ash (FA), a mixture of 70% SR, 20% FA, and 10% clay was formed to produce soda residue soil (SRS). By adding cement and/or lime, four different SRS proportions were prepared. The compaction properties, mechanical properties, and dry–wet stability. Furthermore, the mechanical mechanisms of SRS were explored, and the improvement effect and efficiency of cement and/or lime on the mechanical performance of SRS were analyzed. The results show that the SRS is lightweight and easy to compact and shape, which is conducive to construction. Compared to cement, lime has a greater impat on the compaction properties of SRS. The mechanical properties of SRS are enhanced after adding cement and/or lime; the unconfined compressive strength (UCS), California Bearing Ratio (CBR), and resilient modulus all increase significantly. The UCS, CBR, and resilient modulus of SRS with different proportions all increase with the increase of compaction degree; the CBR and resilient modulus can meet the requirements of the subgrade, and the UCS can meet the requirements of the base and sub-base. The contribution rate of cement per unit amount is better than that of lime to the mechanical performance of SRS. As dry–wet cycles increase, the dry–wet stability of SRS with different proportions first increases and then decreases, which is affected by hydration and dry–wet deterioration together, with a critical cycle number for the strength transition. The excellent mechanical performance of SRS benefits from the gradation and chemical action. The particles of SR, FA, and clay can complement each other and perform an interlocking action. Therefore, SRS has a good gradation and forms a dense and stable structure. Also, the chemical reactions between materials are very important. The cement and/or lime have a hydration and gelling effect, FA and clay participate in pozzolanic reactions, and SR and FA have certain alkali-activated effects. [ABSTRACT FROM AUTHOR]

In order to effectively utilize red mud and reduce its occupation of land resources, as well as its impact on the environment, experiments were conducted to develop stabilized soil materials using nano-SiO2 synergistically modified red mud and to investigate the curing mechanism of stabilized soil. The unconfined compressive strength, microscopic morphology, and curing mechanism of the red mud-based stabilized soil materials with different amounts of modified materials were investigated. The test results show that after 7 days of curing, the unconfined compressive strength of red mud-based stabilized soil meets the compressive strength requirement of road base material when nano-SiO2, gypsum, and cement are synergistically modified. In such cases, the soil structure has the lowest fracture rate and the best structural compactness when the amount of nano-SiO2 is 1%. It is found that the needle-like and columnar calcium alumina in the modified red mud-based stabilized soil increases, and the binding energy of hydration product ions in the modified material is improved. The chemical curing mechanism of modified red mud-based stabilized soil includes hydration reaction, pozzolanic reaction, promotion effect of nano-SiO2, and enhancement effect of gypsum. On this base, a model of the early start hydration process of red mud-based stabilized soil promoted by nano-SiO2 is established. [ABSTRACT FROM AUTHOR]

In recent years, chemical solidification has been widely utilized to enhance problematic soil's finer structural integrity and macrostructural properties. Nevertheless, most study pertains to the soil of the temperate zone, and comparative investigation on highly plastic laterite soil stabilized with strong electrolyte is very limited. The objective of this study is to ascertain the performance of Hexa-hydrated magnesium chloride (MgCl2·6H2O or bischofite), an Eco-friendly stabilizer, on the macro- and micro-structural description of highly plastic laterite soil collected from Warangal, Telangana state of India. The Bischofite was incorporated with laterite soil in different dosages (2–12%) for optimal soil bischofite mix. The effect of hydrogen ions on the structural arrangement and mechanical modification of clay with curing periods was investigated by PH. The plasticity is changed substantially by the addition of bischofite. Standard compaction tests, Strength of unconfined samples (UCS), and shear strength tests were accustomed to scoping the strength aspects of untreated and treated samples. There was a noticeable improvement in soil strength when stabilized with the selected additive. The degree of strength improvement was triple that of the untreated sample at optimal additive content (8%). Furthermore, the result of consolidation tests at optimal additive content showed resistance to compressibility than natural soil. In addition, combined XRD, SEM, EDS, FTIR, and BET surface area showed that the macrostructural and microstructural advancement of laterite soil could be ascribed to the early physical support in the soil structure due to the optimal additions. Subsequently generated (M-A-H) weak cementitious Hydrates play a vital role using pozzolanic reaction with active ions. The results show that the microstructure is strongly related to mechanical solidification. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Various emerging carbon capture technologies depend on being able to reliably and consistently grow carbon dioxide hydrate, particularly in packed media. However, there are limited kinetic data for carbon dioxide hydrates at this length scale. In this work, carbon dioxide hydrate propagation rates and conversion were evaluated in a high pressure silicon microfluidic device. The carbon dioxide phase boundary was first measured in the microfluidic device, which showed little deviation from bulk predictions. Additionally, measuring the phase boundary takes on the order of hours compared to weeks or longer for larger scale experimental setups. Next, propagation rates of carbon dioxide hydrate were measured in the channels at low subcoolings (<2 K from phase boundary) and moderate pressures (200–500 psi). Growth was dominated by mass transfer limitations until a critical pressure was reached, and reaction kinetics limited growth upon further increases in pressure. Additionally, hydrate conversion was estimated from Raman spectroscopy in the microfluidics channels. A maximum value of 47% conversion was reached within 1 h of a constant flow experiment, nearly 4% of the time required for similar results in a large scale system. The rapid reaction times and high throughput allowed by high pressure microfluidics provide a new way for carbon dioxide gas hydrate to be characterized. [ABSTRACT FROM AUTHOR]

Ceramisite lightweight concrete has excellent performance and relatively light self-weight characteristics. At the same time, the recent development of green high-performance concrete and prefabricated components has also brought the abundant utilization of these mineral mixture. An interfacial transition zone exists between the hardened cement paste and the aggregate, which is the weakest part of the concrete, characterized by high porosity and low strength. In order to study the effect of slag content on the interfacial transition zone in lightweight high-strength concrete, experiments were designed to replace cement with slag at different contents (0%, 5%, 10%, 15%). A series of studies was conducted on its macro-strength, microstructure, and composition. The results indicated that the addition of slag improved the porosity and width of the interfacial transition zone. Adding slag did not reduce the thickness of the concrete interfacial transition zone significantly at 3 d, but it led to significant improvement in the thickness of the interfacial transition zone at 28 d, and the thickness of the interfacial zone at 28 d was reduced from 19 μm to 8.5 μm, a reduction of 55%. The minimum value of microhardness in the slurry region of the interfacial specimens also increased from 19 MPa to 26 MPa, an increase of 36%. In addition, the structural density of the interfacial region was further increased, resulting in varying degrees of improvement in the macroscopic anti-splitting strength. One of the important reasons for this phenomenon is that the addition of slag optimizes the chemical composition of the interface and promotes the continuation of the pozzolanic reactivity, which further enhances the hydration at the interface edge.

This study investigated the effects of lithium slag and iron tailings on the hydration mechanism of Basic Oxygen Furnace (BOF) slag cement paste with the addition of 0.06% diethanol-isopropanolamine (DEIPA). This study examined the fluidity, compressive strength, pore solution pH, and hydration products of BOF slag-based composite cementitious materials. The results showed that DEIPA facilitated the conversion from ettringite (AFt) to monosulphate (AFm) and improved the early compressive strength of the BOF slag–cement mortar. Incorporating lithium slag into the DEIPA-containing BOF slag–cement system promoted AFt formation, increased calcium-silicate-hydrate production, and enhanced the microstructure. BOF slag, lithium slag, and iron tailings exhibit synergistic effects in cement pastes. BOF slag and lithium slag provided the reactive components SiO2 and Al2O3. In the early hydration stages, the iron tailings primarily served as fillers, accelerating the system’s reactions.

The use of raw materials from the recovery of construction waste is frequent. In this study, the waste is obtained from degraded railway ballast, made up of siliceous minerals. This material is added directly to the mixtures to replace part of the cement, forming a good quality cementitious product. The pozzolanic reaction is studied within the waste/lime system in a solid phase and water system for one year. Reaction products such as stratlingite, layered double hydroxide-type compounds, hydrated tetracalcic aluminate, and gels appear. The formation of stratlingite and gels was favored throughout the reaction. The reaction was monitored, calculating the saturation index.

Recycled aggregate concrete (RAC) includes recycled concrete aggregates (coarse and/or fine) as substitutes for natural aggregates as an approach to achieving a circular economy. Some concerns remain about its performance, including the carbonation resistance. The higher porosity of recycled concrete aggregates is logically a disadvantage, but the analysis must address many other factors. This paper provides an in-depth examination of recent advances in the carbonation performance of RAC. The emphasis is on factors that influence CO2 diffusion and the carbonation rate, e.g., the replacement ratio, source concrete quality, interfacial transition zone features, residual portlandite content, and porosity. The influences of previous treatments, combined action with supplementary cementitious materials, and loading conditions are also discussed. The replacement ratio has a significant impact on the carbonation performance of concrete, but it is also dependent on other factors. During carbonation, the physical effects of the porosity of the aggregate and the physical–chemical effects of the portlandite content in the adhered mortar are particularly important. The residual portlandite is especially significant because it is the primary hydration product responsible for the alkaline reserve for carbonation and the potential pozzolanic reaction, which are per se competing factors that determine the carbonation rate. [ABSTRACT FROM AUTHOR]

Fly ash and slag are widely used in cement production. The effect of alkali sulfates in clinker on hydration and hardening of cement blended with fly ash and slag is studied. The results of hydration heat evolution, hydrates analysis and mechanical properties indicate arcanite (K2SO4), thenardite (Na2SO4), aphthitalite (3K2SO4·Na2SO4, K3NS4) and Ca-langbeinite (K2SO4·2CaSO4, KC2S3) in clinker could activate the pozzolanic activity of fly ash and slag, facilitating the appearance of the second hydration peak in the initial hydration period, and promote the hydration and hardening properties of blended cement. The adverse effects of alkali sulfates in clinker are alleviated with the addition of fly ash and slag; this can be attributed to the dilution and filler effects of supplementary cementitious materials (SCMs), as well as the effect of the alkali sulfates activating fly ash and slag. Arcanite, thenardite and aphthitalite (K3NS4) provide a better activating effect on mortar with slag than fly ash mortar to increase compressive strength and reduce drying shrinkage when the content of alkali sulfates is less than 0.6% sodium oxide equivalent (Na2Oeq). [ABSTRACT FROM AUTHOR]

Using ceramic tile waste as a soil stabiliser in road construction is a potential solution to dispose of the waste material while providing a cost-effective alternative to traditional stabilising agents. The ceramic tile waste, when crushed and mixed with soil, helps to improve the strength and durability of the road base. However, the effectiveness of the ceramic tile waste as a soil stabiliser depends on the type and size of ceramic tiles used and the soil properties being stabilised. This study investigated the effect of ground tile waste on the plasticity, compatibility, and mechanical properties such as the unconfined compressive strength (UCS), indirect tensile test (IDT), flexural test (FS), and microstructural analysis. A range of soil mixtures was prepared by adding the different percentages of fine tile waste (TW): 5% to 40%. Including tile waste in the soil led to a decrease in its water-holding capacity, reducing the optimum moisture content required for optimal compaction. Meanwhile, the maximum dry density increased. The UCS, IDT, and FS improved when the optimum 15% of TW was used in the mixes. However, the strength decreased after 20% of the TW addition. This effect was particularly pronounced in the presence of excessive TW contents in soil samples without a pozzolanic reaction. Reusing tile waste as a soil stabiliser can significantly reduce the costs of purchasing new materials and helps to conserve natural resources and reduce the environmental impact of waste disposal. [ABSTRACT FROM AUTHOR]

Calcium carbide residue (CCR) can be reutilized to solidify the loess for road construction as a base or subbase due to its rich Ca(OH)2 facilitating pozzolanic reaction with water and soil particles. This study examines the effect of curing time, CCR contents, and dry unit weights on the tensile strength (Rt) of CCR-stabilized loess through the splitting tensile test. Aiming to predict the Rt values, the ratio of porosity (n) controlled by compacted effort and initial volumetric CCR content (Liv), namely n/Liv , was chosen as a prediction parameter and then modified to n/Liv0.064 for compatible variation rate with Rt values. A prediction model for the splitting tensile strength of CCR-treated soil was proposed considering the modified ratio n/Liv0.064 and curing days. The results indicate that Rt values showed a nearly linear positive correlation with CCR contents and dry unit weights, logarithmic increase with the extension of curing time, but no apparent relationship with the ratio n/Liv. The modified ratio n/Liv0.064 can reflect the trend of Rt values at different curing days since the coefficients of determination were almost greater than 0.90 except for the specimens cured for seven days. The proposed prediction model had a good fit for laboratory data with 97% acceptability and close to 3% error. It can be applied for estimating the Rt values of CCR-stabilized loess using curing time and an optimized ratio of porosity and initial volumetric CCR content. From the aspect of practical engineering, the reutilization of CCR can reduce construction costs, waste disposal costs, and environmental pollution. [ABSTRACT FROM AUTHOR]

Aim of study was to verify the effect of temperature on the pozzolanic reactivity of thermally activated attapulgite and sepiolite samples. Activation temperatures were selected: 650, 700 and 750 °C for attapulgite and 800, 825 and 850 °C for sepiolite. Content of pozzolanic reactive SiO2 and Al2O3 after thermal treatment and the amount of Ca(OH)2 consumed in the pozzolanic reaction were measured. It should be noted that a higher activation temperature improves the reactivity of attapulgite and sepiolite. The upper limit for the increase in the pozzolanic reactivity of these materials is the formation of enstatite and the deactivation of silica. In addition to reactive decomposition products, series of minerals formed in the reactions of attapulgite and sepiolite with impurities present in them are also observed. [ABSTRACT FROM AUTHOR]

Global carbon dioxide emissions can be attributed to Portland cement production; thus, an alternative cementitious system is essential to reduce cement demand. Ceramic waste powder (CWP), which contains high proportions of silica and alumina, has emerged as a promising alternative because of its chemical composition. This review discusses the potential of CWP as an alternative cementitious system and its effects on the physical, mechanical, and durability properties of cementitious systems. The findings revealed that the utilization of CWP in cementitious systems has positive effects on their physical, mechanical, and durability properties owing to the chemical composition of CWP, which can act as a filler material or contribute to the pozzolanic reaction. A pozzolanic reaction occurs between the silica and alumina in the CWP and calcium hydroxide in the cement, resulting in the production of additional cementitious materials such as calcium silicate hydrates and calcium aluminate hydrates. These additional materials can improve the strength and durability of cementitious systems. Various studies have demonstrated that CWP can be effectively used as a partial replacement for cement in cementitious systems. This can reduce the carbon footprint of construction activities by reducing the demand for Portland cement. However, the optimal amount and particle size of CWP have not been fully determined, and further research is required to optimize its use in cementitious systems. In addition, the technical and economic challenges associated with the use of CWP in construction must be further investigated to ensure its effective implementation. [ABSTRACT FROM AUTHOR]

Growing environmental awareness and scarcity of natural resources are forcing the world to migrate from linear to circular economies. The possibility of partially replacing cement with ceramic-based waste from construction and demolition waste (C&DW) is a government and industry focus. The present study analyzes the effects of including finely ground complete walls of ceramic blocks (including masonry mortars) as supplementary cementing materials (SCM) on the physical, mechanical, and transport properties (water absorption and permeability) of concrete. The replacement ratio employed was 25% by weight of cement. Studies of the hydration evolution of cement pastes support the described properties of concretes. The findings reveal that the ground ceramic-based waste from C&DW stimulates hydration at all ages. Initially, this stimulation is predominantly physical (filler effect), but in later stages, it becomes chemical (pozzolanic reaction). Based on the results obtained in this study, it is possible to produce concrete with mechanical properties comparable to those of conventional concrete at 28 days. [ABSTRACT FROM AUTHOR]

The use of silica fume as a partial replacement for Ordinary Portland Cement provides a wide variety of benefits, such as reduced pressure on natural resources, reduced CO2 footprint, and improved mechanical and durability properties. The formation of more stable crystallographic phases in the hardened cement paste can promote resistance to concrete attacks. However, using coarse silica fume may result in lower expenses and shorter workdays. In this work, coarse silica fume was used as a partial replacement of cement, by weight, at 3%, 5%, and 7%, and it was used as limestone filler at different particle sizes. The size of coarse silica fume used was 238 μm. The microstructural, compositional analysis, and crystalline phase content of mixed cements at different ages were evaluated. The addition of coarse silica fume and limestone promoted pore refinement of the composites and increased the calcium and silica content. The filling effect of fine limestone and coarse silica fume particles, as well as the formation of CSH gel, was found to be the main reason for the densified microstructure. The contributions of combined coarse silica fume and limestone improve the stability of CSH gels and pozzolanic reaction. [ABSTRACT FROM AUTHOR]

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, a time-dependent key parameter is proposed to estimate the unconfined compressive strength (UCS) of a typical sand treated with cement and zeolite. To this end, the data of a series of unconfined compression tests were collected from previous works on the sand specimens treated with the addition of stabilizers, including either only cement or cement and percentages of cement replacement with natural zeolite, in multiple curing times. Afterward, a state-of-the-art time-dependent active composition (ACnew) parameter was defined to predict the UCS characteristics of the treated soils. In the definition of the ACnew parameter, a hyperbolic function was employed to correlate the development of pozzolanic reaction triggered by active components (CaO and SiO2 + Al2O3) with time. Through the proposition of the ACnew parameter, the impact of the time-dependency of the zeolite treatment on the behavior of the stabilized specimens and the development of the pozzolanic reaction as well as the variation of UCS with increasing curing time are adequately justified. Finally, it is indicated that incorporating porosity (η) and ACnew in the form of power functions represents a considerable estimation of the UCSs of the studied treated sand in comparison to previous empirical correlations. [ABSTRACT FROM AUTHOR]

Steel slag and ground blast furnace slag show good wear resistance, which is suitable for improving the abrasion performance of pavement concrete. This work presents an investigation of the activation of Na2SO4, Na2CO3 and Na2SiO3 on the GBFS-SS composite pavement concrete. The results showed that both Na2SO4 and Na2SiO3 can promote the strength development of the GBFS-SS composite cementitious system. Na2CO3 shows limited improvement in the strength of GBFS-SS composite paste. The GBFS-SS composite paste activated with Na2SiO3 and Na2SO4 combination shows hydration products of ettringite, portlandite and amorphous C-A-S-H gel. SO42− can accelerate the depolymerization of the aluminosilicate network in GBFS and SS vitreous structure, while SiO32− can only facilitate the pozzolanic reaction of GBFS and SS, but also participate in the hydration to form more C-A-S-H gel. Na2SO4 as the activator can reduce the dry shrinkage of the pavement concrete, while Na2SiO3 as the activator can further improve the compressive strength and abrasion resistance of the pavement concrete. The combined activation of Na2SiO3 and Na2SO4 shows a better effect on improving the performance of pavement concrete than the single Na2SiO3 or Na2SO4 activator. At the optimal content of 3% of Na2SiO3 and 1% of Na2SO4, the pavement concrete obtains the 60 d compressive strength of 73.5 MPa, the 60 d drying shrinkage of 270 × 10−6, the 60 d interconnected porosity of 6.85%, and the 28 d abrasion resistance of 28.32 h/(kg/m2). [ABSTRACT FROM AUTHOR]

In this study, sustainable engineered cementitious composites (ECC) exhibiting high tensile strength as well as high tensile strain capacity were successfully developed by incorporating polyethylene (PE) fiber, local recycled fine aggregate (RFA), and limestone calcined clay cement (LC3). The improvement in tensile strength and tensile ductility was attributed to the self-cementing properties of RFA as well as the pozzolanic reaction between calcined clay and cement. Carbonate aluminates were also generated owing to the reaction between calcium carbonate in limestone and the aluminates in both calcined clay and cement. The bond strength between fiber and matrix was also enhanced. At the age of 150 days, the tensile stress-strain curves of ECC containing LC3 and RFA shifted from a bilinear model to a trilinear model, and the hydrophobic PE fiber exhibited hydrophilic bonding performance when embedded in RFA-LC3-ECC matrix, which could be explained by the densified cementitious matrix as well as the refined pore structure of ECC. Moreover, the substitution of ordinary Portland cement (OPC) by LC3 resulted in energy consumption and equivalent CO2 emission reduction ratios of 13.61% and 30.34%, respectively, when the replacement ratio of LC3 is 35%. Therefore, PE fiber-reinforced RFA-LC3-ECC demonstrates excellent mechanical performance as well as considerable environmental benefits. [ABSTRACT FROM AUTHOR]

This study presents utilisation of high-volume fly ash (HVFA) in the design of self-compacting concrete (SCC) containing alternative aggregate particles. Class F fly ash was used in a binary blend of Portland cement at a fixed dosage of 50% by weight of powder, and natural coarse and fine aggregates were replaced with coarse and fine recycled concrete aggregates (RCAs), respectively, at replacement levels of 0, 50 and 100% by volume. The durability properties of the SCC mixes were studied using the rapid chloride penetration test, initial surface absorption test and capillary suction test. The results of the study showed that the concrete mix made with replacement of natural coarse aggregates with 50% coarse RCAs, the concrete mix made replacement of natural fine aggregates with 50% fine RCAs and the concrete mix made with replacement of both natural coarse and fine aggregates with the respective RCAs at 50% replacement levels had satisfactory performance without compromising their fresh and hardened-state properties. Furthermore, the incorporation of HVFA in SCCs improved the hardened-state properties at later ages of curing due to the secondary pozzolanic reaction. [ABSTRACT FROM AUTHOR]

Aiming at the problem of repeated repair of concrete caused by the damage of concrete structure repair system in a sulphate environment, the quicklime modified sulphoaluminate cement (CSA)–ordinary Portland cement (OPC) –mineral admixture composite repair material was utilised to obtain the law and mechanism of quicklime, improving the mechanical properties and sulphate resistance of composite repair materials. In this paper, the effects of quicklime on the mechanical properties, as well as sulphate resistance of CSA–OPC–ground granulated blast furnace slag (SPB) and CSA–OPC–silica fume (SPF) composites, were studied. The findings reveal that the addition of quicklime improves the stability of ettringite in SPB and SPF composite systems, promotes the pozzolanic reaction of mineral admixtures in composite systems, and significantly increases the compressive strength of both SPB and SPF systems. The 8 h compressive strength of SPB and SPF composite systems increased by 154% and 107%, and the 28 d compressive strength enhanced by 32% and 40%. After the quicklime was added, the formation of C-S-H gel and calcium carbonate in SPB and SPF composite systems was promoted, the porosity was reduced, and the pore structure was refined. The porosity was reduced by 2.68% and 0.48%, respectively. The mass change rate of various composite systems under sulphate attack was reduced, and the mass change rate of the SPCB30 and SPCF9 composite systems decreased to 0.11% and −0.76% after 150 dry–wet cycles. Additionally, the mechanical strength of different composite systems under sulphate attack was improved, so that the sulphate resistance of different ground granulated blast furnace slag and silica fume composite systems was improved. [ABSTRACT FROM AUTHOR]

Limestone Calcined Clay Cements, LC3, allows CO2 emissions savings up to 40%. The resulting binders have competitive mechanical performances after a week. However, the reactivity of LC3 at early ages is slow and should be improved. Here, we use a multitechnique approach to help in the understanding of early age reactivities which were measured by calorimetry, Frattini assay, and mechanical strengths. The disorder in the kaolinites was quantified by powder diffraction. Some footprints of the local disorder in the resulting metakaolin have been investigated by synchrotron pair distribution function (sPDF). It is concluded that Al-O interatomic correlation position and intensity in the sPDF of the calcined kaolinitic clays could be an additional good descriptor to follow early age reactivity. The results were complemented by 27Al MAS-NMR studies. The rate of the pozzolanic reaction at early ages is governed by the particle size, surface area, and local disorder of metakaolin. [ABSTRACT FROM AUTHOR]

The harnessing of glass waste, which is slow to decompose and has high recycling costs, is in the interest of supporting and stimulating a balanced construction pattern that is interdependent on the living environment. Consumable food and drink bottles are one of these forms of waste that can be calibrated to meet desired specifications. Controlled low-strength materials with low and deliberate strength for future excavation have highly desirable rheological properties, active hardening, and zero or rare separation of materials can be maintained with waste glass substitution. In this study, an experimental evaluation was commenced to estimate the practicality of waste glass (fine and coarse powder) by replacing fly ash and natural sand with it to control low-strength materials. A sum of seven slurry blends was intended by employing several ratios (10%, 30%, and 50%) of fine and coarser waste glass. Some characteristics of plasticity and hardness were observed, such as fine glass decreased flowability. In contrast, coarser glass decreased dramatically, exceeding the minimum limit of 20%, which necessitated the use of superplasticizer in a proportion that corresponds to the increase in the replacement. Unit weight slightly increased with fine glass substitution, but in the Coarser substitution, a steady decrease occurred. The compressive strength of 28 days in fine glass replacement is less than the reference mixture, but it exceeded it at 90 days. A mixture incorporating coarse waste glass was higher at 28 days and developed at 90 days.

Natural Hydraulic Lime (NHL) has exceptional application in restoring ancient buildings compared to Portland cement and conventional air-hardening lime, but the characteristic of slow early performance development limits its fields of application. This paper studied the physical and mechanical properties, hydration exothermic properties, phase composition and transformation, and microstructure evolution of slag powder/metakaolin composite NHL during the early hardening process. The influence of slag powder/metakaolin on the hardening process and performance development of NHL are systematically evaluated. Results show that slag powder can improve the fluidity of NHL-based mortar; slag powder/metakaolin generates calcium aluminate hydrate (C3AH6), calcium carboaluminate hydrate (C4A?H11) and calcium silicate hydrate (C—S—H) through pozzolanic reaction to promote the setting and hardening of NHL-based materials and significantly improve their compressive and flexural strength. This study provides reference for promoting the application of pozzolanic material composite NHL in the restoration of ancient buildings.

The influences of mechanically activated fly ash on the microstructure and thermal behaviour of atmospheric-cured concrete panels have been evaluated. For this purpose, comparative analyses of concretes prepared with and without addition of raw and milled fly ashes were performed. The raw fly ash was activated with an attrition mill for 1 h. Cylindrical concrete specimens with and without 20% fly ash substitution and large concrete panels with the same compositions were prepared. Mechanical properties of the concrete specimens were measured after 3, 7, 28 days, 2 and 4 months. After preparation the cylindrical specimens were cured in water while the concrete panels were kept in an open atmosphere outside the building for 1 year.The 28-day compressive strengths of the non-fly ash added cylindrical concrete specimen was 61.1 MPa, raw and mechanically activated fly ash added specimens were 54.4 and 64.7 MPa, respectively. Microstructural and thermal studies of the concrete panel were performed in the core drilled specimens after 1 year curing. The compressive strength of the core drilled specimens was 26.6, 25.4 and 35.9 MPa for the non-fly ash added, raw and mechanically activated fly ash added concrete panels.A beneficial pozzolanic reaction and improved mechanical properties of the milled fly ash-substituted concrete cured under harsh weather conditions were observed and determined by differential thermal analysis-thermogravimetry and mercury intrusion porosimetry. Improved mechanical properties of the milled fly ash added panel indicates its potential applicability in industrial practice due to the simplicity of the process.

The effects of replacing OPC with three types of calcium sulfoaluminate (CSA) cements (40 wt%, 20 wt%) were studied. The results were broadly consistent with previously published data, with a few notable exceptions. Because of the production of ettringite, setting times were decreased. The maximal hydration temperature increased in concretes containing 40 wt% CSA but dropped in concretes with 20 wt% replacement. The drop was caused by a lack of accessible sulfates, which limited the synthesis of ettringite. In comparison to OPC concretes, the inclusion of additional anhydrite and calcium oxide was related with a delayed formation of the second temperature peak. Their excess slowed the calcium aluminate and belite reactions and reactivated the synthesis of ettringite, C–S–H, and portlandite. The effects of aluminum hydroxide were also indicated as potentially significant, although this was not proven experimentally in this study. The slightly lower compressive strength reported for mixes containing 40 wt% CSA was associated with better-formed ettringite. The same was identified as the key to lowering total shrinkage in mixtures containing 40 wt% CSA and increasing for lower CSA replacement levels. In that case, the insufficient amount of ettringite generated resulted in expansion that was insufficient to alleviate or compensate for the developed shrinkage. [ABSTRACT FROM AUTHOR]

The present work aims to evaluate expansive soil stabilization using different additives. Twenty soil mixtures consisting of 10%, 20%, 25%, and 30% zeolitic tuff (ZT) with 2%, 4%, and 6% lime in various combinations were used to stabilize the soil for pavement subbase application. A comprehensive test program, including Atterberg's limits, compaction, unconfined compression strength (UCS), California Bearing Ratio (CBR), resilient modulus, and permanent deformation, was performed on natural and stabilized soil specimens. Scanning electron microscopy (SEM) supplied with energy-dispersive X-ray spectroscopy (SEM/EDX) was used to confirm the study findings. Adding ZT increases the availability of the silica and alumina needed for the pozzolanic reaction; test results revealed that adding ZT increases the maximum dry unit weight, CBR, UCS, resilient modulus, decreases plasticity, and permanent deformation. As such, ZT can improve the physical and mechanical properties of lime-stabilized soil as a pavement's subgrade and subbase layers. [ABSTRACT FROM AUTHOR]

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Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Portland cement (PC) is a material that is indispensable for satisfying recent urban requirements, which demands infrastructure with adequate mechanical and durable properties. In this context, building construction has employed nanomaterials (e.g., oxide metals, carbon, and industrial/agro-industrial waste) as partial replacements for PC to obtain construction materials with better performance than those manufactured using only PC. Therefore, in this study, the properties of fresh and hardened states of nanomaterial-reinforced PC-based materials are reviewed and analyzed in detail. The partial replacement of PC by nanomaterials increases their mechanical properties at early ages and significantly improves their durability against several adverse agents and conditions. Owing to the advantages of nanomaterials as a partial replacement for PC, studies on the mechanical and durability properties for a long-term period are highly necessary. [ABSTRACT FROM AUTHOR]

Curing temperature affects the compressive strength of cement paste systems via the pozzolanic reaction. However, different processes, climates, and weather conditions often result in different initial curing temperatures. The relationship between curing temperature and compressive strength is still an underexplored domain. To explore the effect of curing temperature on calcium hydroxide (CH)-based fly ash composites, fly ashes from different carbon sources were used to make CH-based composites, and the compressive strength, reaction rate, CH content, and C-S-H generation were analyzed. The correlation between the reaction rate and C-S-H content was analyzed. High-temperature curing improved the compressive strength of the cement paste system by affecting the CH-based reaction rate in the initial stage, with the highest initial reaction rate reaching 28.29%. However, after cooling to constant temperature, high-temperature curing leads to a decrease in CH and C-S-H content. The average decrease rate of calcium hydroxide content under high temperature curing is 38%, which is about 2.38 times that of room-temperature curing conditions. This led to a decrease in the compressive strength of the cement paste. Therefore, the performance of CH-based fly ash composites produced by low-temperature curing was superior to that of composites produced by high-temperature curing. [ABSTRACT FROM AUTHOR]

This study proposed to introduce a combination of crushed granite (CG), superabsorbent polymer (SAP), and expansive agent (EA) into ultrahigh-performance concrete (UHPC) to mitigate the early autogenous shrinkage of UHPC without causing deterioration of its workability and mechanical performance. To this end, the effects of CG, SAP, and EA individually and their combinations on the workability, compressive strength, and autogenous shrinkage of UHPC were investigated. The results showed that CG, EA, and SAP all reduced the autogenous shrinkage of UHPC. However, the addition of CG and EA deteriorated the workability of UHPC, while the introduction of SAP decreased the compressive strength of UHPC. When CG (14.7% vol.), 1% EA, and 0.15% SAP were combined (CG+EA-1+SAP-0.15), UHPC showed the best overall performance. Specifically, the 7-day autogenous shrinkage of the CG+EA-1+SAP-0.15 group was 296.1 με , which was 68% lower than the reference group (without CG, EA, and SAP); the 28-day compressive strength was slightly improved; and the slump flow was only 1.6% lower than that of the reference group, which was negligible. The results of thermogravimetry analysis showed that SAP could enhance the hydration of portland cement and EA, and could also promote the pozzolanic reaction of ground granulated blast furnace slag and silica fume. The results of mercury intrusion porosimetry demonstrated that the microstructure of UHPC was refined due to the enhancement of hydration by internal curing of SAP. Besides, when CG, EA, and SAP were combined, the total porosity of UHPCs first decreased and then increased when the dosage of SAP increased. Specifically, the total porosities of the reference, CG+EA-1+SAP-0.1, CG+EA-1+SAP-0.15, and CG+EA-1+SAP-0.2 groups were 9.6%, 9.2%, 5.5%, and 9.4%, respectively. The CG+EA-1+SAP-0.15 group had minimum porosity, which was 42.87% lower than reference group. The above results demonstrated that the combined use of CG, SAP, and EA can effectively mitigate the early autogenous shrinkage of UHPC, but the optimal ratio between EA and SAP should be further studied. [ABSTRACT FROM AUTHOR]

Metakaolin (MK) is a high-quality, reactive nanomaterial that holds promising potential for large-scale use in improving the sustainability of cement and concrete production. It can replace cement due to its pozzolanic reaction with calcium hydroxide and water to form cementitious compounds. Therefore, understanding the dissolution mechanism is crucial to fully comprehending its pozzolanic reactivity. In this study, we present an approach for computing the activation energies required for the dissolution of metakaolin (MK) silicate units at far-from-equilibrium conditions using the improved dimer method (IDM) and the transition-state theory (TST) within density functional theory (DFT). Four different models were prepared to calculate the activation energies required for breaking oxo-bridging bonds between silicate or aluminate units. Our results showed that the activation energy for breaking the oxo-bridging bond to a silicate neighbor is higher than that to an aluminate neighbor due to the ionic interaction. However, for complete silicate tetrahedra dissolution, a higher activation energy is required for breaking the oxo-bridging bond to the aluminate neighbor compared to the silicate neighbor. The findings provide methodology for missing input data to predict the mesoscopic dissolution rate, e.g., by the atomistic kinetic Monte Carlo (KMC) upscaling approach. [ABSTRACT FROM AUTHOR]

Heavy structures built on untreated collapsible soil remain susceptible to failure due to abrupt changes in the soil structure upon wetting. Industrial wastes like cement kiln dust (CKD) can be used to solve this problem. For this study, undisturbed and disturbed collapsible soil samples were collected from Thal Haro arid area, Punjab, Pakistan. CKD was mixed up to 20% to stabilize the collapsible soil with a maximum of 28 days of curing time. To perform strength tests and collapsible potential tests, samples were remolded at optimal water content and maximum dry unit weight. The CKD content exponentially improves the unconfined compression strength, deformation modulus, and soaked California bearing ratio; however, it marginalizes the ductility of treated soil. With the addition of CKD, the strain at failure and deformability index is significantly decreased. Moreover, for microstructural characteristics comparison, X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDAX) analyses were performed on untreated and treated samples. Due to the addition of CKD, XRD and EDAX results show the new peaks of calcium and calcium silicate, respectively, in treated samples. The formation of the new element and compound indicates the generation of bonds among soil partials owing to the hydration and pozzolanic reactions which is also verified by the SEM results. The SEM analyses manifest the conversion of the dispersed and silt-dominated structure of the native collapsible soil to a reticulated structure without micropores due to the addition of CKD. [ABSTRACT FROM AUTHOR]

The deep mixing method is considered one of the most popular ground improvement techniques, which cement is commonly used as a cementitious material. However, the use of cement resulted in high cost and high carbon footprint. Utilizing bottom ash, a by-product from electricity power plant, as a green stabilizer material is of interest. This paper studied the effect of bottom ash and ground bottom ash on the properties of cement stabilized soft Bangkok clay. The variables included initial water content, clay/binder ratio, cement/BA ratio, and curing time. The unconfined compressive strength test, scanning electron microscope, cost, and CO2 emission were assessed. The results showed that the strength decreased with the increase in initial water content because of the bleeding effect and poor particle bonding. The mixes with 10%BA and 10%GBA achieved the highest 7-day and 28-day strengths for all clay/binder ratios. The strength of sample with GBA was higher than that with BA due to the higher reactivity of the GBA. For BA, the mixes with 60clay/40binder exhibited sufficient strength passing the Thailand's Department of Highways requirement for cement column materials. In the case of GBA, the lower binder content mix with 70clay/30binder met the strength requirement. According to the SEM analysis, the improvement of the matrix was observed and confirmed the higher pozzolanic reaction of GBA and the resulting higher strength from the higher surface area. This research thus showed that the cement-BA could be used as a low-cost and low-carbon binder for the stabilization of clay. [ABSTRACT FROM AUTHOR]

The use of mineral additives, arising from industrial waste, for construction materials such as cement has environmental and economic importance. Also, there is a vital gap between research and issued standards in the wetting-drying field which is well-known as one of the most important corrosive environmental conditions. Only a few pieces of research report non-air entrained fly ash substituted composites exposed to freezing-thawing. In this study, 20% of cement was replaced with fly ash and 60 wetting-drying or freezing-thawing cycles were applied to the samples. For microstructural investigation, cement paste prisms were prepared in two groups of control and fly ash-cement mixtures with the dimension of 40 x 40 × 160 mm. Additionally, 150 x 150 × 150 mm cubes were molded to study the mechanical properties of fly ash-containing concrete subjected to the wetting-drying or freezing-thawing cycles. First series of control and fly ash-added samples after a 28-day curing period were exposed to the purposed cycles. Similarly, the second and third series after 56 and 90 days were exposed to wetting-drying or freezing-thawing cycles. Based on the obtained results, fly ash-containing samples performed better than control mixtures after a 90-day curing period with/without application of wetting-drying cycles since excessive CSH gel was produced as a prominent product of pozzolanic reaction decreased porosity of the mixtures and increased adherence between particles. After the exposure to freezing-thawing cycles, control composites displayed better performance than fly ash-containing samples at early ages. As an important achievement of this study, pozzolanic reactions required at least 90 days to be completed under normal curing conditions at the standard temperature. Due to the required long curing time, partial cement replacement with fly ash can be an efficient alternative for the production of prefabricating elements used in marine construction or other constructions exposed to cold weather. [ABSTRACT FROM AUTHOR]