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Simplifying the synthesis process and preparing a new type of shrinkage reducing agent (SRA) with a low dosage and high efficiency are beneficial for promoting the development of SRA and its application in cement-based materials. This study aims to synthesize three novel polymer-type SRAs with diverse structures through free radical copolymerization and to investigate their performance and working mechanisms in cement-based materials. Results clearly showed that the three synthesized SRAs reduced the surface tension of pore solution, and increased the flowability of cement paste. The SRAs-1 with butyl resulted in higher flowability of cement paste due to lower surface tension. Their addition at a low dosage of 0.5% by cement mass effectively mitigated the shrinkage of cement mortar. Among the three, SRAs-1 with butyl exhibited a higher capability of reducing drying shrinkage due to lower surface tension, lower porosity in the range of 2.5–50 nm, and lower total porosity. [ABSTRACT FROM AUTHOR]

In this study, a PCE polymer was synthesized by copolymerizing isopentenyl polyoxyethylene ether (TPEG) with trans-2-butenedioic acid (FA). Thereafter, the dispersing effect of the resulting PCE polymer was evaluated via spread flow tests in cement pastes containing varying amounts of montmorillonite (MMT). The ultimate objective of this study was to investigate the mode of action between PCE polymer and MMT in cement paste and thus provide strategies to minimize the negative impact of MMT on PCE efficiency. The adsorbed amount of the PCE polymer linearly increased with the increasing dosage of MMT, whereas the spread flow of cement pastes linearly decreased with the increasing dosage of MMT. X-ray diffraction (XRD) results revealed that PCE/MMT ratio was critical in the sorption process, where electrostatic attraction played a significant role at low PCE/MMT ratios, whereas side chain intercalation dominated at high PCE/MMT ratios. The reduction in flowability caused by PCE is primarily attributed to the competitive adsorption of MMT in cement paste. [ABSTRACT FROM AUTHOR]

One of the perspective approaches for converting natural and technogenic mineral sources into eco-friendly cementitious materials and composites is through alkali activation technology. Over the past few decades, an extensive resource base of mineral sources has been established for alkali-activated materials (AAMs). This resource base is continuously expanding with the rapid development of alkali-activation theory and technology, as well as ongoing studies by numerous research groups around the world. In addition, the sustainable development and circularity paradigm, which aims for a "zero-waste" future, has heightened the importance of focusing on the upcycling of large-tonnage wastes, such as construction and demolition wastes, including concrete wastes (CWs). The challenges associated with effectively upcycling CWs through geopolymerization technology, including diverse chemical-mineralogical compositions, factors influencing suitability as a sole or complementary precursor, and approaches to maximize recycling value, are discussed in this review. It is suggested to categorize CWs as high- and low-Ca types. Further research should be conducted to determine optimal composition criteria, techniques to enhance reactivity, establish durability aspects, and reduce alkaline activator content. These efforts would greatly contribute to advancing the raw material base, reducing production process complexity and costs, and enhancing both the environmental and economic potential of CW-based geopolymers. • Concrete wastes are promising precursors for alkali-activated materials. • Concrete wastes should be categorized as high- and low-calcium precursors. • Polymerization activity increases proportionally to cement paste/aggregates ratio. • Activation techniques make concrete wastes more resilient for the future. [ABSTRACT FROM AUTHOR]

Internal curing by superabsorbent polymer (SAP) is an effective method to mitigate the autogenous shrinkage of cement‐based materials with low water‐to‐cement ratio (w/c). In this study, the water absorption/desorption kinetics of SAP were studied quantitatively in blended cement pastes with ultra‐low w/c. An absorption process at a rate of 0 to 6 g/(g h) was calculated at early ages. After that, SAPs showed mainly two distinct water desorption behaviors with a rate of 0 to 1.1 g/(g h), which was mainly governed by the osmotic pressure and capillary pressure triggered by the drop of internal relative humidity (IRH). The size and amount of SAP played a predominant role in controlling its absorption and desorption kinetics in the cement paste. Compared with ordinary Portland cement, a different desorption process with a higher release rate was noticed in binary and ternary cement pastes, primarily due to the changes in osmotic pressure resulting from the acceleration of cement hydration by silica fume at early ages. Overall, the mitigation of autogenous shrinkage is found to be highly dependent on SAP's absorption and desorption kinetics. [ABSTRACT FROM AUTHOR]

The primary goals of the present study are to decrease CO 2 emissions and minimize the excessive consumption of natural resources associated with cement production. The main natural resource was diatomite (DIO), a naturally abundant material found in several regions of Mexico. Four different hybrid cement (HC) mixtures were prepared using NaOH, while maintaining a consistent OPC percentage of 10 % across all the mixtures. The obtained results demonstrate the exceptional performance of one of these HC mixtures, surpassing OPC properties in terms of compressive strength at 1, 7 and 28 days, with values of 28.8, 47.16 and 62.9 MPa, respectively. The outstanding HC mixture underwent thorough confirmation through a range of analyses, such as TG, FTIR, SEM and EDX. This innovative HC composite offers several solutions to reduce CO 2 emissions and conserve natural resources currently wasted in cement manufacturing, making it a compelling choice for various industrial and construction applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Three polycarboxylates with different comb structures (i.e., the same degree of polymerization in side chains but different main chains) were synthesized via radical polymerization reaction at room temperature. The effect of polycarboxylates on the surface tension and the flowability in cement pastes was determined. The best product was selected to study its effects on the hydration heat evolution, compressive strength, autogenous shrinkage, and drying shrinkage of cement pastes with different kinds and contents of supplementary cementitious materials. The results showed that with the increase of molar ratio between AA and TPEG to 6 : 1, we could synthesis the best product. When the water-binder ratio was 0.4, with the increase of polycarboxylates, the cement hydration heat evolution had been slowed down, and the more the dosage was, the more obvious the effect was. Adding supplementary cementitious materials to cement under the same experimental conditions also played a mitigation role in slowing down the hydration heat. When the water-binder ratio was 0.3, supplementary cementitious materials could increase the strength of cement by 24.5% in maximum; its autogenous shrinkage and drying shrinkage could be decreased, respectively, by 60.1% and 21.9% in the lowest. [ABSTRACT FROM AUTHOR]

• The influence factors on chloride binding of AACs are studied. • The Langmuir isotherm suits better for chloride adsorption of most of AACs. • The chloride binding is predominantly affected by the chloride concentration. • The Friedel's salt only presents in AAS samples after adsorption equilibrium. • The bound chloride of AACs increases with the increased w/b ratio. In this study, the effects of slag/fly ash ratio, Na 2 O concentration, silicate modulus of activators and water/binder ratio on chloride binding of alkali-activated slag/fly ash cements (AACs) are studied, using the binding isotherms. The Langmuir isotherm suits better for chloride adsorption of most of AACs, and the amount of bound chloride is predominantly influenced by the chloride concentration. The Friedel's salt only presents in alkali-activated slag samples after adsorption equilibrium. An appropriate slag/fly ash ratio could improve the chloride binding capacity due to the physical adsorption of N-A-S-H. The chloride binding of AACs decreases with the increased Na 2 O concentration but increases with the increased water/binder ratio, which is believed to be related to the OH− concentration in pore solutions. [ABSTRACT FROM AUTHOR]

• The effects of silicate modulus (Ms) on carbonation of AACs are studied. • The carbonation rate and the amount of CaCO 3 decrease with the increase of Ms. • The carbonation behaviors of high-Ca systems are different from the low-Ca systems. In this study, the effects of silicate modulus of activators (Ms) on carbonation of alkali-activated slag/fly ash cements are studied and compared between natural (0.03–0.04% CO 2) and accelerated (1% CO 2) carbonation conditions, via XRD, FTIR and TG/DTG techniques. Carbonation results in the decalcification of the C-A-S-H gels and the formation of calcium carbonates and silica gels, while the N-A-S-H gels are essentially constant after carbonation. The main calcium carbonate phase after carbonation is calcite, and the increase of Ms leads to the generation of vaterite and aragonite. The carbonation behaviors of low-calcium system (20% slag) are different from the high-Ca systems (100% and 60% slag), while the carbonation rate and the amount of calcium carbonates generally decrease with the increase of Ms in all of the studied systems. This investigation provides an in-depth understanding of carbonation mechanisms of alkali-activated cements, and is essential for the establishment of carbonation models and prediction of long-term performances. [ABSTRACT FROM AUTHOR]

Highlights • The physical and chemical effects of limestone powder (LP) were calculated. • The chemical effect of LP was influenced by its particle size and amount of LP at 3d. • The particle size and amount of LP had little effect on its chemical effect at 180d. Abstract The study aims to quantitatively calculate the physical and chemical effects of limestone powder (LP) with four average particle sizes and two amounts in cement pastes by using thermal gravimetric analysis (TGA), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) techniques. At 3d, as the average particle size of LP decreased from 32 to 6 μm, the consumed CaCO 3 content in LP increased from 0.67% to 1.71%, and the chemically reactive portion of LP increased from 1.15% to 2.95%. However, at 180d, the consumed CaCO 3 content and chemically reactive portion of LP was almost 2.4% and 4.2%, respectively. At 3d, as the LP content increased from 25% to 50%, the consumed CaCO 3 content in LP increased from 1.71% to 2.02%, and the chemically reactive portion of LP increased from 2.95% to 3.5%. However, at 180d, the differences of consumed CaCO 3 content and chemically reactive portion of LP between cement pastes with different LP content were limited. The physical and chemical effects of limestone powder on the compressive strength of cement pastes were calculated. At 180d, as the average particle size of LP decreased from 32 to 6 μm, the contribution of chemical effect of LP on the compressive strength of cement pastes increased from 1.01% to 1.08% while the contribution of physical effect decreased from 21.19% to 20.03%. [ABSTRACT FROM AUTHOR]

Abstract The long-term durability and their mechanisms of alkali-activated cement based materials have remained largely elusive. In this paper, carbonation of alkali-activated slag (AAS) mortars activated by NaOH and waterglass with different alkali dosages and silicate moduli has been investigated after exposure to 3 ± 0.2% (v/v) CO 2 at 20 ± 2 °C/65 ± 5% RH for 56 days. The results show that carbonation resistance of the AAS mortars increases with increase of not only alkali dosage but also silicate modulus. In addition to the higher pore solution alkalinity and slag reaction extent, the relatively higher carbonation resistance of the AAS mortars is attributed to the lower porosity and average pore size. The loss of compressive strength for the waterglass activated slag mortars after carbonation is due to decalcification of C-A-S-H phase, whereas the carbonation of katoite contributes to the increase of compressive strength of the NaOH activated slag mortars. [ABSTRACT FROM AUTHOR]

Steel slags are industrial by-products of steel manufacturing, characterized as highly calcareous, siliceous and ferrous. They can be categorized into basic oxygen furnace (BOF) slag, electric arc furnace (EAF) slag, and ladle furnace (LF) slag. They are found to be useful in many fields, such as road construction, asphalt concrete, agricultural fertilizer, and soil improvement. However, better utilization for value-added purposes in cement and concrete products can be achieved. In this paper, an overview of the recent achievements and challenges of using steel slags (BOF, EAF and LF slag) as cement replacement (usually ground into powder form with the size of 400–500 m 2 /kg) and aggregate in cement concrete is presented. The results suggest that the cementitious ability of all steel slags in concrete is low and requires activation. For the incorporation of steel slags as aggregate in concrete, special attention needs to be paid due to the potential volumetric instability associated with the hydration of free CaO and/or MgO in the slags. Studies have indicated that adequate aging/weathering and treatments can enhance the hydrolyses of free-CaO and -MgO to mitigate the instability. Considering the environmental and economic aspects, steel slags are also considered to have a potential use as the raw meal in cement clinker production. [ABSTRACT FROM AUTHOR]

Addition of limestone to Porland cement can significantly increase the hydration and high early strength of Porland cement. However its application in the magnesium phosphate cement is less known. In this paper, magnesium potassium phosphate cement (MKPC) pastes in which magnesium oxide was replaced by up to 30% limestone were studied. The effect of limestone content on the hydration temperature, setting time, compressive strength, and early water stability were investigated. The deterioration mechanism in water was explored by analyzing the pH value of the immersed solution, leached substances, total phosphorus content and microstructural analyses including X-ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TG/DTG) and mercury intrusion porosimetry (MIP). The results showed that addition of limestone into the magnesium phosphate cement matrix accelerated the setting time, decreased the total heat evolution of MKPC, and clearly degraded the strengths. The poor water stability of MKPC with limestone powder might be caused by the poor crystallinity and crystal morphologies of hydration products, worsened pore structure and increased dissolution of hydration products. Considering the materials costs and the strength development, the optimum addition of limestone powder should be no more than 10%. [ABSTRACT FROM AUTHOR]

High performance cement-based materials, such as high or ultra-high performance concrete (HPC or UHPC) have been widely used and still faces the risk of cracking caused by shrinkages, especially autogenous shrinkage. Internal curing is an effective method to reduce or even eliminate autogenous shrinkage and has effects on chemical shrinkage, dry shrinkage, etc. The commonly used internal curing materials include super-absorbent polymer (SAP) and porous materials. Porous materials refer to lightweight aggregate (LWA) and porous superfine powders. In this paper, the internal curing materials has been divided into two categories based on water absorbing mechanism. The effects of these two categories of internal curing materials on shrinkage of high performance cement-based materials are reviewed. The addition of internal curing materials releases internal curing water, postpones the drop of internal RH, and reduces autogenous shrinkage, but increase chemical shrinkage. The addition of internal curing materials with extra water increases drying shrinkage. The mechanisms of shrinkage on internal curing are also summarized and discussed. However, those mechanisms only focus on certain type of shrinkage. To reduce the risk of cracking more effectively, the relationship of different type of shrinkages should be established. [ABSTRACT FROM AUTHOR]

This study investigated the effects of curing regimes (standard, hot water, and steam curing) on mechanical properties of ultra-high performance concrete (UHPC) with different supplementary cementitious materials (SCMs). The flowability, compressive strength, flexural load-deflection relationship, ultimate flexural strength, and toughness of UHPC mixtures with 0, 20%, 40%, and 60% of either ground granulated blast-furnace slag (GGBS) or fly ash, by the mass of cement, were evaluated. Test results indicated that the increase in GGBS or fly ash content had limited or negative influence on the compressive strength of UHPC in terms of curing regime type . For the flexural strength, there existed an optimal SCM content, which was 40% for GGBS and 20% for fly ash. Excessed this dosage could result in a drop in flexural strength and toughness. The hot water and steam curing significantly improved the flexural properties. However, prolonging the standard curing over 28 d led to comparable flexural properties as those under hot water and steam curing showed. The production of UHPC with appropriate GGBS or fly ash content with adequate standard curing, therefore, offers an effective way to obtain satisfactory flexural properties. [ABSTRACT FROM AUTHOR]

The permeability of the cement-based materials can be used as an important indicator of their durability. Surface treatment is a simple way to reduce permeability and improve durability of cement-based materials. This paper studied the effects of fluosilicate and sodium silicate surface treatments on the permeability of cement-based materials using the Autoclam water permeability and water absorption testing method. The experimental results showed that both fluosilicate and sodium silicate surface treatments could effectively reduce the permeability of cement-based materials. However, fluosilicate worked within the first 28days after treatment, while sodium silicate showed more obvious effect at later ages. Autoclam water permeability index exhibited an exponential relationship with the water absorption of the cement-based materials. In addition, mercury intrusion porosimetry result suggested that these inorganic surface treatment agents could reduce the porosity of surface layer of cement-based materials. [ABSTRACT FROM AUTHOR]

This work investigated the effect of carbon dioxide treatment of recycled concrete aggregate (RCA) on the performance of RCA and RCA mortar. The results indicated that carbonation increased the apparent density, and reduced both water absorption and the crushing value of the RCA. The flowability and compressive strength of the RCA mortar were lower than those of natural sand mortar. However, the properties of mortar made with carbon dioxide treated RCA were very similar to those of natural sand mortar. Compared with the mortar made of un-carbonated RCA, the mortar made with carbonated RCA showed increased autogenous shrinkage, reduced drying shrinkage, water absorption, and chloride migration coefficient. Scanning electron microscope (SEM) examination on the interfacial transition zone (ITZ) in the RCA and RCA mortar found that carbonation treatment of RCA not only improved the original ITZ in the RCA, but also improved the newly formed ITZ in the RCA mortar. [ABSTRACT FROM AUTHOR]

Ultra high performance (UHPC) is a new cement based material, and it has aroused interest around the world since it was introduced in the early 1990s. Part I reviewed the theoretical principles, raw materials selection, mixture design and preparation techniques for UHPC. This part II reviewed the hydration, microstructure, mechanical properties, dimensional stability and durability of UHPC. Finally, some needs for future studies of UHPC are suggested. The portlandite of UHPC is much lower than that in the normal concrete. Heat curing could promote secondary hydration between mineral admixtures and Ca(OH) 2 , and xonolite was formed when the temperature was over 250 °C. UHPC has a very low porosity, especially under heat curing. UHPC has a character of high strength, stiffness and superior durability, etc. [ABSTRACT FROM AUTHOR]

This study investigated the flowability, compressive strength, heat of hydration, porosity and calcium hydroxide content of ultra-high-strength concrete (UHSC) with cement–silica fume–slag binder at 20 °C. The composition of the binder was designed using seven-batch factorial design method. The relationships between the binder composition and the properties were expressed in contours. Results showed that proper silica fume content could improve the flowability and compressive strength of UHSC, reduce the porosity and calcium hydroxide content of UHSC. Slag reduced the flowability, compressive strength, porosity, and calcium hydroxide content of UHSC to certain extent. The silica fume and slag demonstrated positive synergistic effects on the flowability and 3 d compressive strength, but have negative synergistic effects on the total heat of hydration, hydration heat when the time is infinitely long( P 0 ), 56 d compressive strength, porosity and calcium hydroxide content of UHSC. [ABSTRACT FROM AUTHOR]

This paper studied the influence of waterglass on the early water stability of potassium magnesium phosphate cement (MKPC). Mass loss and residual strength were used to reflect the water stability of MKPC pastes exposed to different curing conditions. Experimental results indicated that the addition of waterglass could accelerate early hydration of MKPC, reduce the crystallinity of hydration products, and improved the pore structures significantly. The early water stability of MKPC was greatly improved due to the significant decreased dissolution of hydration products and pore volume of hardened MKPC. [ABSTRACT FROM AUTHOR]

• The effects of slag/fly ash ratios, Na 2 O% and Ms of activators on the sulfate attack of AACs are studied. • Upon the Na 2 SO 4 attack, the C-A-S-H gel structures of AACs do not change basically. • The MgSO 4 attack on AACs is severe due to the dissolution of alkali and the migration of Mg2+. • Gypsum is the main product in AACs upon the MgSO 4 attack. • The effect of Ms on the sulfate resistance of AACs is related to the slag/fly ash ratios. In this work, the effects of slag/fly ash ratios, Na 2 O concentration, and silicate modulus (Ms) of activators on the reaction mechanism of sulfate attack on alkali-activated slag/fly ash cements are elucidated by XRD, FTIR, and TG/DTG analysis. To accelerate the sulfate attack process, the alkali-activated cements (AACs) were crushed into particle samples before immersion in the Na 2 SO 4 and MgSO 4 solutions. The results show that upon the Na 2 SO 4 attack, the C-A-S-H gel structures of AACs do not change basically. However, the MgSO 4 attack on AACs is severe due to the dissolution of alkali and the intrusion of Mg2+. Gypsum is the main product in AACs upon the MgSO 4 attack, and the amount of brucite decreases with the incorporation of fly ash. The NaOH-activated slag (Ms = 0) has a relatively higher MgSO 4 resistance compared with the Na 2 SiO 3 -activated slag, while it is the opposite when the fly ash replacement level increases to 80%. [ABSTRACT FROM AUTHOR]

Durability is one of the most important considerations regarding the design of new concrete structures in aggressive environments. Thaumasite sulfate attack (TSA) is one durability consideration. This paper reviews the features of TSA, factors affecting TSA, thaumasite formation mechanisms, and prevention measures. Finally, some needs for future studies are also suggested. TSA can completely destroy the cementitious binding ability of concrete by transforming it into a mush. Many factors affect thaumasite formation and TSA. The four primary factors affecting TSA on portland cement-based materials are low temperatures (below 15°C) and the presence of sulfates, carbonates, and moisture. Apparently, the dissolution-precipitation mechanism can be used to explain most phenomena during TSA. A procedure for field studies is also proposed. Both material compositions and surrounding environments should be considered for the prevention of TSA in concrete structures. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews the chloride binding of cement-based materials subjected to external chloride environments. Chloride ion exist either in the pore solution, chemically bound to the hydration products, or physically held to the surface of the hydration products. Chloride binding of cement-based material is very complicated and influenced by many factors, such as chloride concentration, cement composition, hydroxyl concentration, cation of chloride salt, temperature, supplementary cementing materials, carbonation, sulfate ions and electrical field etc. Four different types of binding isotherms, namely linear, Langmuir, Freundlich and BET binding isotherm have been proposed to describe the relationship between free and bound chloride, none of which can accurately express the relationships between free and bound chloride within the whole concentration range. Freundlich binding isotherm seems to be the most approximate one. However, some field data fit linear isotherm well. This may be ascribed to the leakage of hydroxyl ion. Many service life prediction models based on diffusion mechanism alone have been proposed during the past two decades. If chloride ion binding is not considered in the models, it underestimates the predicated service life. [Copyright &y& Elsevier]

Abstract: Copper slag is a by-product obtained during matte smelting and refining of copper. The common management options for copper slag are recycling, recovering of metal, production of value added products such as abrasive tools, roofing granules, cutting tools, abrasive, tiles, glass, road-base construction, railroad ballast, asphalt pavements. Despite increasing rate of reusing copper slag, the huge amount of its annual production is disposed in dumps or stockpiles to date. One of the greatest potential applications for reusing copper slag is in cement and concrete production. Many researchers have investigated the use of copper slag in the production of cement, mortar and concrete as raw materials for clinker, cement replacement, coarse and fine aggregates. The use of copper slag in cement and concrete provides potential environmental as well as economic benefits for all related industries, particularly in areas where a considerable amount of copper slag is produced. This paper reviews the characteristics of copper slag and its effects on the engineering properties of cement, mortars and concrete. [Copyright &y& Elsevier]

Abstract: This paper deals with the effects of several factors, such as CO2 pressure, curing time, water-to-cement ratio and continued curing after CO2 curing on temperature profiles, CO2 curing degree and strength of concrete. Results indicated that the accelerated reactions between CO2 and cement minerals happen mainly during the first 15min regardless of CO2 pressure and pre-conditioning environment. CO2 curing degree and strength increased as the CO2 pressure and curing time increased. The concrete specimens should have a water-to-cement ratio greater than certain value so as to facilitate the moulding of concrete products and to achieve a high CO2 curing degree. CO2 cured specimens will continue to gain strength due to the hydration of cement minerals unreacted during the CO2 curing if the specimens are kept in moist environment. [Copyright &y& Elsevier]

Abstract: The use of recycled waste glasses in Portland cement and concrete has attracted a lot of interest worldwide due to the increased disposal costs and environmental concerns. Being amorphous and containing relatively large quantities of silicon and calcium, glass is, in theory, pozzolanic or even cementitious in nature when it is finely ground. Thus, it can be used as a cement replacement in Portland cement concrete. The use of crushed glasses as aggregates for Portland cement concrete does have some negative effect on properties of the concrete; however, practicle applicability can still be produced even using 100% crushed glass as aggregates. The main concerns for the use of crushed glasses as aggregates for Portland cement concrete is the expansion and cracking caused by the glass aggregates. This paper summarizes the progresses and points out the directions for the proper uses of waste glasses in Portland cement and concrete. [Copyright &y& Elsevier]

Abstract: This paper reviews progresses on the use of alkali-activated cements for stabilization/solidification of hazardous and radioactive wastes. Alkali-activated cements consist of an alkaline activator and cementing components, such as blast furnace slag, coal fly ash, phosphorus slag, steel slag, metakaolin, etc., or a combination of two or more of them. Properly designed alkali-activated cements can exhibit both higher early and later strengths than conventional portland cement. The main hydration product of alkali-activated cements is calcium silicate hydrate (Ch name="sbnd" />H) with low Ca/Si ratios or aluminosilicate gel at room temperature; Ch name="sbnd" />H, tobmorite, xonotlite and/or zeolites under hydrothermal condition, no metastable crystalline compounds such as Ca(OH)2 and calcium sulphoaluminates exist. Alkali-activated cements also exhibit excellent resistance to corrosive environments. The leachability of contaminants from alkali-activated cement stabilized hazardous and radioactive wastes is lower than that from hardened portland cement stabilized wastes. From all these aspects, it is concluded that alkali-activated cements are better matrix for solidification/stabilization of hazardous and radioactive wastes than Portland cement. [Copyright &y& Elsevier]

Solidification/stabilization (S/S) is often used to treat waste or to remediate contaminated sites. Many people feel S/S is just a process to consolidate waste into a solid product for disposal using cementing materials. This article describes designing a cement-based formula for solidification/stabilization of wastes or contaminated soils from aspects of both the cement chemistry and the environmental chemistry. The discussion includes the following key points: (1) compatibility between cement and waste materials; (2) chemical fixation of contaminants; (3) physical encapsulation of contaminated waste and soils; (4) durability of the treated waste or soil; (5) leachability of contaminants from the treated waste or soil; and (6) cost-effectiveness of S/S. [ABSTRACT FROM AUTHOR]

Steel slag is a byproduct from either the conversion of iron to steel in a basic oxygen furnace, or the melting of scrap to make steel in an electric arc furnace. This paper reviews the production, processing, and characteristics of steel slag, and its use as a cementing component in different cementing systems. The chemical composition and cooling of molten steel slag have a great effect on the physical and chemical properties of solidified steel slag. Steel slag with high basicity and being cooled properly can exhibit cementing property. Ground steel slag has been used in several different cementing systems. The use of steel slag in these cementing systems results in some advantages over conventional cements. At the moment, most steel slag is being used as unbound aggregate for ashphalt concrete pavement in many countries. However, the use of steel slag as a cementing component should be given a priority from technical, economical, and environmental considerations. [ABSTRACT FROM AUTHOR]

The rapid chloride permeability test (RCPT)—American Society of Testing and Materials (ASTM) test method C1202 or American Association of States Highway and Transportation Officials (AASHTO) test method T277—is virtually a measurement of electrical conductivity of concrete, which depends on both the pore structure characteristics and pore solution chemistry of concrete. This paper discusses the effects of several factors, such as cement composition, replacement of cement with supplementary cementing materials and inclusion of aggregate, on the electrical conductivity or RCPT results of hardened cement mortars and concrete. Analyses based on published results have indicated that all the three factors may have significant effects on the chemistry and specific conductivity of concrete pore solution, which has little to do with the transport of ions in the solution. Thus, RCPT is not a valid test for evaluation of permeability of concretes made with different materials or different proportions. [Copyright &y& Elsevier]

Ladle slag fines consist mainly of γ-C2S, which does not show cementitious property in water, but can exhibit significant cementitious property in the presence of alkaline activators at room temperatures. This study deals with the hydraulic reactivity of ladle slag fines under autoclaving conditions. The results indicate that ladle slag fines cannot be used as cementing material alone because of the presence of free lime in ladle slag. The combination of a ladle slag fine and a siliceous material, such as silica flour (ground quartz), can eliminate the soundness problem and give very high strength. The introduction of a small amount of Portland cement or hydrated lime into ladle slag fine–silica flour system can increase strength significantly. Lime is more effective than Portland cement due to the presence of Al in Portland cement. The autoclaving temperature should be higher than 175 °C and the time for constant temperature does not need to be more than 4 h to achieve satisfactory strength. Finally, seven batches of experiments are designed to plot isostrength contours for ladle slag fine–cement–silica flour and ladle slag fine–hydrated lime–silica flour ternary systems. [Copyright &y& Elsevier]

Nearly 60% of the electricity in the USA is produced by coal-fired plants, which results in the production of a large quantity of coal combustion residues, among which coal fly ash is the major component. Many applications have been developed for coal fly ash. The use of coal fly ash as a cement replacement in concrete is the most attractive one because of its high volume utilization and widespread construction. However, the replacement of cement with coal fly ash in Portland cement concrete usually increases the setting time and decreases the early strength of concrete. The addition of chemical activators such as Na[sub 2]SO[sub 4] or CaCl[sub 2] accelerates pozzolanic reactions and changes pozzlanic reaction mechanisms between fly ash and lime, which results in decreased setting time, accelerated strength development, and increased strength of materials containing fly ash, especially with a high percentage of fly ash. The other promising cements include alkali-activated fly ash and alkali-activated fly ash-ground blast furnace slag cements, which can exhibit very high strength in the presence of proper alkaline activators. Thus chemical activation of reactivity of fly ash is an effective method to increase the use of fly ash in concrete. [ABSTRACT FROM AUTHOR]

Investigates the effects of several factors on the hydration and properties of lime-pozzolan cements. Effect of lime content on water requirement and initial porosity; Effect of types of lime on hydration chemistry; Reaction degree of lime in lime-pozzolan cement pastes cured at 50 degrees centigrade.

• Simplex design method was used to elucidate the composition-dependent mechanism. • Composition changes and properties were correlated via graphical visualization. • Relationships between the paste composition and its properties were developed. This paper aims to elucidate the effect of changes in the mix composition on the properties of Portland cement (PC)-metakaolin (MK)-limestone (LS) ternary system. To achieve this, the mixture proportion was optimized using the simplex design method and its effect on the properties of the binder was evaluated experimentally and correlated via graphical visualization. Experimental results confirmed the enhancement and acceleration of kinetics of cement hydration by LS and MK. However, a higher porosity was noticed at early age and was attributed to the high reactivity of MK which hindered it from acting as an effective filler. Therefore, the correlation between the optimum mix design and compressive strength was found to be dependent on the paste age. The findings of this paper would contribute to a better understanding of the dependence of the properties of PC-MK-LS ternary system on its composition. [ABSTRACT FROM AUTHOR]

This paper investigates the influences of supplementary cementitious materials (SCMs) on the compressive strength and chloride ion permeability of cement mortar with ultra-low water to binder ratio. The applicable of rapid chloride migration (RCM) test on the evaluation of chloride penetration resistance is studied. Test results show that with the decreased specimen thickness and extended standing time during water saturation process, the chloride migration coefficient of cement mortars with ultra-low water to binder ratio can be measured with sufficient testing duration. Within a specific range of replacement level, the replacement of cement with SCMs such as slag, fly ash and silica fume significantly densifies the pore structure and increase the compressive strength and chloride penetration resistance of cement mortar, especially for the cement mortar with silica fume. When more than one type of SCMs are incorporated, the cement mortars with silica fume and slag or fly ash show superior performance than other mixtures.A good linear relationship exists between compressive strength and porosity of cement mortars. Compared to the total porosity, the chloride migration coefficient is more affected by the volume of pores with diameter larger than 20 nm within cement mortars. [ABSTRACT FROM AUTHOR]

• The effects of Na 2 O% and w/b ratio on the carbonation of AACs are studied. • In carbonated AAS, CaCO 3 increases when Na 2 O% increases from 4% to 8%. • In AACs with 60% slag, the decreased w/b ratio improves the carbonation resistance. • In AACs with 20% slag, the increased Na 2 O% reduces the carbonation degree. In this study, the effects of Na 2 O concentration and water/binder (w/b) ratio on the phase evolution and carbonation of alkali-activated slag/fly ash cements are studied. After sealed curing for 28 days, the alkali-activated cement powders were performed accelerated carbonation for 7, 14, 35, 60, and 120 days, at CO 2 concentrations of 1.0 ± 0.2%, 20 ± 2 °C, and RH = 65 ± 2%. In alkali-activated slag at w/b ratio = 0.5, when the Na 2 O concentration increases from 4% to 8%, the amount of calcium carbonates after carbonation increases due to a higher activation degree of slag and the decalcification of more C-A-S-H gels, but the crystallinity of calcium carbonates decreases. At a fixed Na 2 O concentration of 6%, when the w/b ratio decreases from 0.5 to 0.3, the formation rate of calcium carbonates and the crystallinity of calcium carbonates decrease. When the content of slag is 60%, the formation rate of calcium carbonates decreases with the increased Na 2 O concentration from 6% to 8%, due to the higher reaction degree of fly ash and the formation of more N-A-S-H gels; and the amount of calcium carbonates increases with the decreased w/b ratio. When the content of slag is 20%, the increased Na 2 O concentration could decrease the formation rate of calcium carbonates significantly, but the effect of the w/b ratio is limited. [ABSTRACT FROM AUTHOR]

• The microstructure and interfacial properties of cement paste are studied. • The modifications of electrical parameters due to chloride penetration are studied. • The properties of EDL are discussed by the obtained capacitance. • The calculated EDL thickness is correlated to the chloride concentration in EDL. In this paper, the characteristics of AC impedance spectroscopy of cement paste immersed in chloride solution were measured and analyzed with a proposed equivalent circuit model. The elements in the proposed equivalent circuit, including the resistance of interface between electrode and specimens, resistance of continuous and discontinuous pore, capacitance of solid phase and electrical double layer (EDL) were discussed. The results showed that the resistance of interface between electrode and testing specimen was much lower than that of cement paste. With the increase of chloride concentration in the soaking solution, the resistance of continuous gradually decreased due to the higher conductivity of chloride solution. Stripped out the impacts of concentration of pore solution on resistance of pores, the resistance of continuous pore increased firstly due to the decrease of continuous pore volume from the formation of Friedel's salt. However, the resistance of discontinuous pores gradually decreased with the increase of soaking solution concentration due to the transformation of continuous pores to discontinuous pores. The reaction between chloride ions and hydration products and formation of Friedel's salt decreased the porosity of cement pastes and led to higher capacitance of solid phase. Based on an idealized two-plate capacitor model for EDL, the thickness of EDL was calculated from the measured capacitance. The decrease of EDL thickness with chloride concentration in soaking solution was in agreement with the results of chloride contents in EDL obtained from pore solution expression test. [ABSTRACT FROM AUTHOR]

Pore solution expression is a widely accepted approach to extract pore solution of cement-based materials by appllying high pressure. In this study, the variations of pore solution distribution and chloride content in cement pastes before and after pore solution expression were examined. The results showed that the value of chloride concentration index N c were mostly higher than 1.0 for cement pastes immersed in NaCl solution, and decreased with the chloride concentration of soaking solution and water-to-binder (w/b) ratio. During the pore solution expression, the pores larger than 40 nm were totally removed and the porosity of smaller pore was decreased. Based on a proposed physical model on structure of cement paste, the value of N c was calculated according to the variations of pore structure and chloride content during pore solution expression. The calculated results showed similar trend as the experimental results obtained by pore solution expression method. [ABSTRACT FROM AUTHOR]

Effect of diethanolisopropanolamine (DEIPA) and ethyldiisopropylamine (EDIPA) at dosages of 0.02 % and 0.05 % on hydration and strength development of cement-fly ash-limestone ternary blend is investigated. Results indicate that both dosages of DEIPA or EDIPA promote the chemical effect of limestone and the hydration of aluminates from cement and fly ash to form carboaluminates due to their complexation effect, especially 0.05 % of EDIPA. For silicates hydration, 0.02 % of DEIPA or EDIPA accelerate it with more C–S–H gel formation while 0.05 % of DEIPA or EDIPA retard it due to the excessive aluminates hydration and carboaluminates formation at 3 d. However, both dosages of DEIPA and EDIPA promote silicates hydration at 28 d. Besides, DEIPA or EDIPA at both dosages can refine the pore structure with decreased porosity due to the promoted hydration of aluminates and/or silicates and formation of hydration products, although DEIPA and EDIPA exhibit air entraining effect to cause larger pores (>1000 nm). As a result, 0.02 % of DEIPA or EDIPA increase compressive strength of the blend mortar at both 3 and 28 d while 0.05 % of DEIPA or EDIPA slightly decrease it at 3 d but increase it at 28 d. It can be concluded that DEIPA contributes to higher early strength while EDIPA contributes to higher later strength of the ternary blend at both dosages. [ABSTRACT FROM AUTHOR]

A differential impedance analysis method considering constant phase element (CPE) was proposed for cement-based materials. Results indicated that the method is very accurate for the identification circuit of single capacitive loop. For series circuit of double capacitive loops, the method can accurately identify all impedance parameters when ratio ( q ) of the two time constants is large. For series and parallel circuits of double capacitive loops, even when q is close to 1, number of the capacitive loop can be identified accurately. The method can selectively identify the variation, frequency range and frequency dependence of the impedance parameters of cement-based materials; it can also explain why when two capacitive loops exist in a Nyquist plot of cement-based materials, only one can be observed by the naked eye. The method is beneficial for establishing a reasonable equivalent circuit of impedance spectroscopy with a CPE behavior, especially when q is very small. [ABSTRACT FROM AUTHOR]

In this study, the error of stray impedance during measurement and interpretation of the AC impedance of cement-based materials was evaluated based on a proposed reasonable correction method. The results indicated that the stray impedance produces approximately 60% and 35% modulus errors at 15 MHz frequency, and 1.68–55.30% and 10.72–153.58% errors of the interpreted parameters for 210-d and 3-d curing concrete, respectively. The stray impedance of the two electrodes and the extra shorting wire introduced in the traditional correction method ( Z ei ) produce approximately 45% and 15% modulus errors at 15 MHz frequency, and 0.94–82.81% and 49.03–96.71% errors of the interpreted parameters for 210-d and 3-d curing concrete, respectively. The proposed method eliminates the Z ei and contains only extra introduced contact resistance between the shorting wire and the two electrodes ( R cls ). However, the R cls produce less than 1% modulus and the interpreted parameters errors, indicating that the proposed method is accurate. [ABSTRACT FROM AUTHOR]

Alkali activation is a highly active and rapidly developing field of activity in the global research and development community. Commercial-scale deployment of alkali-activated cements and concretes is now proceeding rapidly in multiple nations. This paper reviews the key developments in alkali-activated materials since 2011, with a particular focus on advances in characterisation techniques and structural understanding, binder precursors and activation approaches, durability testing and design, processing, and sustainability. The scientific and engineering developments described in this paper have underpinned the on-going scale-up activities. We also identify important needs for future research and development to support the optimal and appropriate utilisation of alkali activated materials as a component of a sustainable future construction materials industry. [ABSTRACT FROM AUTHOR]

This study investigated the effect of wet carbonated recycled cement paste powder (RCPP) on the rheological properties of cement pastes. The results showed that wet carbonated RCPP decreased the cement paste's setting time and flowability, increased its yield stress and plastic viscosity, and changed its thixotropy. The high absorption capacity of the silica gel in the carbonated RCPP was the most dominant factor influencing the rheological properties of the paste. The absorption capacity of silica gel was dependent on its pore structure, specific surface area, and the amount of hydroxyl groups on its surface. These properties varied with the carbonation method, time, temperature, and CO 2 flow rate. The use of monoethanolamine as the aqueous solution for wet carbonation was found to be an effective approach to mitigate the adverse effect of carbonated RCPP on the rheological properties of cement paste. • Carbonated recycled cement paste powder deteriorated the rheological properties of the paste. • The absorption capacity of silica gel mainly governed the rheological properties of the paste. • The absorption capacity of silica gel was dependent on its pore structure and surface properties. • Monoethanolamine mitigates the negative effect of carbonated recycled cement paste powder on the paste'rheology. [ABSTRACT FROM AUTHOR]