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Cattle manure ash (CMA) is an industrial waste produced from the combustion of cattle manure. This research examined the effect of added CMA produced at combustion temperatures of 500 °C, 650 °C and 800 °C on the workability and mechanical properties of magnesium phosphate cement (MPC). The obtained data indicates that CMA decreases workability and mechanical properties of MPC to which it is added. However, relatively higher combustion temperature in CMA preparation can diminish the adverse effect that CMA exerted on mechanical properties and workability of MPC. CMA promotes the formation of struvite in the hydration reaction of MPC. [ABSTRACT FROM AUTHOR]

The use of recycled construction and demolition (C&D) materials in unbound and cement stabilized pavement base/subbase applications has generated growing interest in recent years. C&D materials consisting of crushed brick (CB), recycled crushed aggregate (RCA), and reclaimed asphalt pavement (RAP) have been investigated in unbound and cement stabilized pavement base/subbase applications. However, the high carbon footprint of using cement for pavement base/subbase stabilization has led to this research to seek alternative low-carbon binders. This study evaluates the behavior of C&D materials when stabilized with geopolymers. Fly ash (FA) and ground granulated blast furnace slag (S) were used as pozzolanic binders and a different alkaline activator solution to pozzolanic binder ratio was tested. A maximum of 4% of dry weight of soil was used for geopolymer stabilization of the C&D materials. The binders used were either 4% FA, 2% FA+ 2% S, or 4% S. The geotechnical engineering and strength properties of these geopolymer-stabilized C&D materials were evaluated to ascertain their performance for pavement base/subbase applications. Elastic modulus, compressive strength, and resilient modulus of the blends were tested and analyzed in this research. Both the resilient modulus of the C&D materials and compressive strength were found to increase as a result of geopolymer stabilization. Geopolymer stabilization was found to be most effective for RCA. Higher compressive strength will be achieved by slag-based geopolymer stabilization when compared with fly ash--based geopolymer stabilization. The effect of alkaline activator to pozzolanic binder ratio on the enhancement of geotechnical properties of C&D materials was also analyzed. The performance of the geopolymer-stabilized C&D materials was furthermore compared with that of traditional cement-stabilized C&D materials. Geopolymer-stabilized RCA and RAP were found to be a viable and sustainable option for the stabilization of future pavement bases/subbases. [ABSTRACT FROM AUTHOR]

A two-phase experimental study on the effect of simultaneous partial replacement of cement and fine aggregate with fly ash on the mechanical and time-dependent properties of high-volume fly ash concrete (HVFAC) is presented. The results of the first phase of the study show that it is possible to make structural grade HVFAC with 50% of cement and an additional 30% of fine aggregate replacement that has a similar compressive strength to that of the control cement concrete and with adequate workability. In the second phase of the study the mechanical and time-dependent properties of HVFAC with a mass of fly ash of 50-70% of the total mass of cementitious materials were tested. The results show that with the increase in fly ash content the compressive strength of HVFAC increased by 22% on average at all ages tested. With the exception of the early-age compressive strength, it was found that the European standard EN 1992-1-1:2004 provisions for ordinary cement concrete underestimate the mechanical properties and significantly overestimate the shrinkage and creep of HVFAC. Better correlation with experimental results was obtained using different coefficients developed for HVFAC. [ABSTRACT FROM AUTHOR]

The Frattini test and strength activity index (SAI) test have been commonly used methods to assess the pozzolanic activity of pozzolan by measuring its reaction extent, which would be affected by the sulfate content in pozzolan and the cement used. This study investigates the effect of sulfate content in sulfate-rich fly ash on the test results regarding pozzolanic activity by means of the Frattini test and SAI test; three fly ashes with different sulfate contents are used and their sulfate contents are further increased by adding calcined gypsums. There is significant correlation between the test results of the pozzolanic activity and the sulfur trioxide content of the cement-fly ash system, no matter whether the sulfates came from cement or fly ash. However, current methods may confound the test results regarding the pozzolanic activity of sulfate-rich fly ash. It is suggested that the sulfur trioxide content of the cement-fly ash system should be kept constant when the Frattini test and SAI test are selected to evaluate the pozzolanic activity of sulfate-rich fly ash or to compare with other fly ashes and pozzolans. [ABSTRACT FROM AUTHOR]

The effect of the combination of fly ash and silica fume on the water resistance of Magnesium–Potassium Phosphate Cement (MKPC) was investigated, and the improvement mechanism was discussed based on the micro-analysis of XRD, FSEM and pore structure. The results indicate that, the physical effect of the combination of fly ash and silica fume on MKPC is dominated compared with the chemical effect because of the optimization of pore structure. The combination of fly ash and silica fume leads to higher density and later-age compressive strength of MKPCs compared to those without fly ash and silica fume under air curing and water curing, respectively. The strength retention ratios (namely water resistance) of MKPCs with the combination of fly ash and silica fume at 56 days are found to be significantly higher than those without fly ash and silica fume. [ABSTRACT FROM AUTHOR]

Today, Portland cement substitutes known as supplementary cementitious materials or SCMs are used to improve the performance while reducing the environmental footprint of concrete. There are several factors that impact the amount of SCMs that can be added to concrete while maintaining its basic integrity. This paper describes a newly developed framework for optimizing the substitution of cement with SCMs in concrete. This framework has been developed based on recent testing results and clearly indicates that paying close attention to cement and SCM particle size distributions (PSDs) and the corresponding packing density of the combined ingredients will allow for an optimization of the cement and SCMs in concrete. This framework has been developed on the basis of several independent laboratory studies and can be adapted as a basis for evaluating and optimizing any combination of cement and SCMs. The means to produce cement/SCM blends with the optimized PSDs with existing equipment configurations are also explored. [ABSTRACT FROM PUBLISHER]

This study proposed a new binder as an alternative to conventional cement to reduce the heat of hydration in mass concrete elements. As a main cementitious material, low-heat cement (LHC) was considered, and then fly ash (FA), modified FA (MFA) by vibrator mill, and limestone powder (LP) were used as a partial replacement of LHC. The addition of FA delayed the induction period at the hydration heat curve and the maximum heat flow value (qmax) increased compared with the LHC based binder. As the proportion and fineness of the FA increased, the induction period of the hydration heat curve was extended, and the qmax increased. The hydration production of Ca(OH)2 was independent of the addition of FA or MFA up to an age of 7 days, beyond which the amount of Ca(OH)2 gradually decreased owing to their pozzolanic reaction. In the case of LP being used as a supplementary cementitious material, the induction period of the hydration heat curve was reduced by comparison with the case of LHC based binder, and monocarboaluminate was observed as a hydration product. The average pore size measured at an age of 28 days was smaller for LHC with FA or MFA than for 100% LHC. [ABSTRACT FROM AUTHOR]

A study examining air-entrainment in fly ash concretes combined with different Portland cements (PCs) is described. Tests were carried out (using five PCs, ten fly ashes and a standard chemical reagent (to entrain air)) on paste suspensions (foam index), mortar and concrete to quantify the material effects. Preliminary tests indicated that the foam index increased with the fineness (specific surface area (SSA) (by nitrogen adsorption Brunauer-Emmett-Teller (BET) method)) of the PC used (varied by grinding) with fly ash. Reductions in the property were found with increasing alkali content in the paste suspensions (by sodium hydroxide addition), which tended to be slightly greater with higher SSA/lower alkali content fly ash. Tests on the wider range of PCs and fly ashes gave a strong correlation between their combined SSA and foam index, with their combined alkali content having less effect on the latter. The influence of fineness was again apparent in the mortar tests, which also showed that when PC and fly ash were of comparable SSA, a change in either material had a similar effect on air-entrainment. However, fly ash had an increasing influence as the difference in this between materials became greater. The results also suggest that air losses after mixing tend to increase with the SSA of PC + fly ash (and hence admixture dose). Similar effects were generally noted in the tests made on concrete. A possible approach to controlling air-entrainment in fly ash concrete may therefore be to ensure that its SSA is similar to that of the PC with which it is used. A test method to enable this to be evaluated is suggested. [ABSTRACT FROM AUTHOR]

Palm Oil Fuel Ash (POFA) is used as a supplementary cementitious material in concrete. Using different percentages of POFA leads to a non-linear variation among the characteristics of concrete. This study aims at developing an empirical model to predict the compressive strength of concrete using POFA as a cement replacement material and other properties of the concrete such as the slump and modulus of elasticity using an artificial neural network. Mixtures of concrete were selected with water-to-binder ratios of 0.50, 0.55 and 0.60, and 10%, 20%, 30% and 40% of the cement content was POFA. The 28-day compressive strength was tested, and the experimental results show that 0%-20% of POFA inclusion in the concrete mixtures has the most positive effects on the compressive strength. Then, a three-layer feed forward-back propagation ANN model with three inputs and three outputs was developed. Finally, the best architecture for the model was trained, tested and validated. [ABSTRACT FROM AUTHOR]

Polymers have been used in cement-based materials to modify important characteristics and properties such as rheology, water-retention ability, cohesion, adhesion, and toughness of fresh and hardened mortars, as well as concretes. In this paper, the characteristic properties of ordinary portland cement (OPC) hydration in the presence of fly ash (FA) and polyvinyl alcohol (PVA) have been studied. The setting times of OPC are prolonged when FA and PVA are added separately or in combination. The compressive strength of FA-blended cement in the presence of PVA at 28 days of hydration is enhanced considerably. An interaction between PVA and hydrating blending cement is expected. Based on the results, the mechanism of action of PVA on the hydration of FA-blended cement is discussed. [ABSTRACT FROM AUTHOR]

Fly ash is used as partial replacement of cement in concrete. The residual carbon in fly ash adsorbs some of the organic concrete admixtures, altering the concrete properties. The use of fly ash in concrete is limited by the lack of adequate fly ash adsorption capacity quantification tools. This paper presents the fly ash iodine number test for the direct measurement of the adsorption capacity of coal fly ash. This test can be used to determine suitability of fly ash for concrete. The developed test was evaluated by comparing the results obtained with the loss on ignition (LOI) and foam index test results for the same fly ash samples. Results show that the fly ash iodine number test can replace current qualitative indicators of adsorption capacity and can be directly used for the characterization and specification of fly ash for the use in concrete. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the nature of permeation properties and pore structure of concrete surface layers containing fly ash. Concretes containing different dosages of fly ash as a replacement for cement (15% and 30% by weight of total cement materials, respectively) were investigated. Concrete without any fly ash added was also employed as the reference specimen. Laboratory tests were conducted to determine the surface layer properties of concrete including chloride transport, apparent water permeability and pore structure. The results demonstrate that incorporation of fly ash, for the early test period, promotes the chloride ingress at the surface layer of concrete but substituting proportions of fly ash may have little impact on it. With the process of chloride immersion, the chloride concentration at the surface layer of concrete with or without fly ash was found to be nearly the same. In addition, it is suggested that the water permeability at the concrete surface area is closely related to the fly ash contents as well as the chloride exposure time. Pore structure was characterized by means of mercury intrusion porosimetry (MIP) test and the scanning electron microscopy (SEM) images. The modification of pore structure of concrete submersed in distilled water is determined by the pozzolanic reaction of fly ash and the calcium leaching effect. The pozzolanic reaction was more dominant at the immersion time of 180 days while the calcium leaching effect became more evident after 270 days. [ABSTRACT FROM AUTHOR]

The effects of material ratio, fly ash, and citric acid on the compressive strength and phase composition of magnesium oxysulfate (MOS) cement have been studied. From these results, when the molar ratio of active MgO/MgSO4 increases from 3 to 5, the compressive strength of magnesium oxysulfate cement increases. When the molar ratio of active MgO/MgSO4 is 3, the main crystal phase contributing to the mechanical strength is 3Mg(OH)2·MgSO4·8H2O; when the molar ratio increases to 5, the main crystal phase is a new magnesium subsulfate that can be expressed as yMg(OH)2·MgSO4·zH2O (Y phase). The compressive strength of MOS cement by adding fly ash decreases from 56.89 to 33.75 MPa (8.251 to 4.895 ksi) by 39.29% when the dosage of fly ash increases to 40%, because SiO2 in fly ash can form magnesium silicate hydrate gel, which can adsorb onto the surface of the Y phase nucleus and inhibit its growth. In the presence of 0.5% weight citric acid (CA), the compressive strength of MOS cement increases, because CA may facilitate the formation of yMg(OH)2·MgSO4·zH2O (Y phase). [ABSTRACT FROM AUTHOR]

The authors investigated the ability of different high-performance concrete (HPC) composites to restrain an alkali-silica reaction (ASR) in the presence of reactive aggregates. They evaluated the effectiveness of different binary and ternary blended cementitious systems comprising optimized contents of pulverized fly ash (PFA) and silica fume (SF) in suppressing ASR expansion. They assessed different mortar mixtures made of different contents of PFA (up to 40%) and SF (up to 15%) with water-to-binder (W/B) ratios of 0.27 for ASR expansion according to standard procedures for accelerated mortar bar test. The results showed a given pessimal combination among the ternary mixtures in which there was an obvious synergistic interaction where ASR expansion was at its minimum level. [ABSTRACT FROM AUTHOR]

This paper investigates the feasibility of developing ultrastrength high-performance flowable concretes made with a high content of supplementary cementitious materials (SCMs). A total of 25 concrete mixtures were prepared and tested. Mixtures were divided into three different groups with water-to-cementitious materials ratios () of 0.3, 0.33, and 0.37, respectively. All mixtures were prepared to achieve a target slump flow equal to or higher than 500 mm (24 in.). The control mixture for each group was prepared with 100% portland cement whereas all other mixtures were designed to have up to 70% of portland cement replaced by a combination of SCMs such as class C or class F fly-ash, granulated blast furnace slag, and silica fume. The properties of fresh concrete investigated in this study include flowability, deformability, filling capacity, air content, and resistance to segregation. In addition, the compressive strength at 1, 7, 28, and 90 days, the unrestrained shrinkage up to 90 days, and the concrete permeability were also investigated. A critical analysis for the properties of fresh and hardened concrete shows that ultrastrength high-performance flowable concrete can be developed with low and up to 70% of cement replaced by supplementary cementitious materials. Properties of such concrete are superior to those of the control mixture made with 100% portland cement. [ABSTRACT FROM AUTHOR]

This paper reports the durability performance of high-volumely-ash (FA)- and slag (S)-incorporated engineered cementitious composites (ECCs) when subjected to mechanical loading and freezing-and-thawing cycles. Composites containing two different contents of FA and slag as a replacement of cement (55 and 70% by weight of total cementitious materials) are examined. To find out the effect of mechanical preloading on the frost durability of ECCs, prism specimens were preloaded up to a certain deformation level under four-point bending loading to generate microcracks. Then, the preloaded and pristine (sound) specimens were subjected to the freezing-and-thawing test in accordance with ASTM C666/C666M. Experimental tests consisted of measuring the change in mass and ultrasonic pulse velocity (UPV) and residual flexural properties of ECC specimens exposed to the freezing-and-thawing cycles up to 300. Test results revealed that the frost resistance of ECCs was significantly influenced by the mineral admixture type and amount and preloading deformation. The deterioration with an increasing number of freezing-and-thawing cycles was relatively more for ECC mixtures with FA than for slag mixtures at the same replacement level. In addition, an increase in the FA replacement rate was observed to exacerbate the deterioration caused by freezing-and-thawing cycles. Apart from some reduction in flexural properties and UPV and an increase in mass loss and residual crack width, the results presented in this study, however, confirm the durability performance of ECC material under freezing-and-thawing cycles, even in cases where the material experiences mechanical loading that deforms it into the strain-hardening stage prior to exposure. It is important to note that this durability of ECCs under freezing and thawing was achieved without deliberate air entrainment, and contrary to conventional concrete, no relationship of frost resistance was found to the air-void structure of the ECC mixtures. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the impact of the fineness and replacement level of a material on the compressive strength, the heat of hydration, and the amount of bound water and calcium hydroxide of the composite cements. The study uses different finenesses of the limestone powder and/or siliceous fly ash (FA)to replace the ordinary Portland cement (OPC). It is found out that the finenesses of OPC and FA play an important role in hydration.

In the last few years, a number of investigations of engineered cementitious composites (ECC) have been carried out, and the mechanical behavior and durability characteristics of this type of composite are now increasingly better understood. The fire-resistant behavior of this specialized concrete, however, has not yet been studied as extensively. This investigation develops important data on the mechanical properties and microstructure of ECC exposed to temperatures up to 800°C (1472°F). In this study, the mechanical properties (the residual compressive strength, stress-strain curve, and stiffness) and mass loss were determined after air cooling, subsequent to temperature exposure. Changes in the microstructure, porosity, and pore size distribution of the firedeteriorated ECC specimens were identified using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) techniques. Test results revealed no significant changes in the mechanical properties for tested specimens exposed to temperatures up to 400°C (752°F) for an hour. Microstructural analysis showed the creation of supplementary pores and channels in the matrix due to polyvinyl alcohol (PVA) fibers melting in the 200 to 400°C (392 to 752°F) temperature range. After a 1-hour exposure to temperatures of 600 and 800°C (1112 and 1472°F), the mechanical performance of fire-deteriorated ECC mixture is similar to or better than that of conventional concrete incorporating polypropylene or steel fibers, despite a significant reduction in compressive strength and stiffness. Moreover, no explosive spalling occurred in any specimens during the fire test. The promising performance of ECC under fire exposure may be due to the presence of PVA fibers and high-volume fly ash (FA). The beneficial influence of FA can be ascribed to the pozzolanic reaction consuming calcium hydroxide in the hydrates. PVA fiber is also beneficial in that it prevents explosive spalling. This introduces additional channels for vaporized moisture in ECC to escape without creating high internal pressure in the material. [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate the possibility of using a combination of ground waste glass and fly ash as a replacement for Portland cement in the manufacture of mortar. Ground waste glass with an average particle size of 100 m was used as cement replacement with a class C fly ash. The influence of waste glass and fly ash combination on the physical properties of cement paste such as the initial and final setting time, volume expansion and water requirement for normal consistency were investigated. The compressive and flexural strength measurements were conducted on the mortar samples at ages of 2, 7, 28 and 56 days. The effect of high temperature at 300, 600 and 900°C on the mortar samples was also investigated. Results indicate that cement paste containing the combination of waste glass and fly ash showed longer setting times than the reference Portland cement. The mortars demanded slightly more water mainly due to the high fineness of the fly ash. It was found that the replacement of Portland cement by a combination of waste glass and fly ash had no remarkable effect on the volume expansion. The mortars containing 5% waste glass + 5% fly ash and 5% waste glass + 10% fly ash satisfy the requirement of strength class 42·5 of the related standard. [ABSTRACT FROM AUTHOR]

The durability of class C fly ash belite cement (FABC-2-W) in simulated radioactive liquid waste (SRLW) rich in a mixed sodium chloride and sulphate solution is presented here. The effect of the temperature and potential synergic effect of chloride and sulfate ions are discussed. This study has been carried out according to the Koch–Steinegger test, at the temperature of 20°C and 40°C during a period of 180 days. The durability has been evaluated by the changes of the flexural strength of mortar, fabricated with this cement, immersed in a simulated radioactive liquid waste rich in sulfate (0.5M), chloride (0.5M) and sodium (1.5M) ions – catalogued like severely aggressive for the traditional Portland cement – and demineralised water, which was used as reference. The reaction mechanism of sulphate, chloride and sodium ions with the mortar was evaluated by scanning electron microscopy (SEM), porosity and pore-size distribution, and X-ray diffraction (XRD). The results showed that the chloride binding and formation of Friedel''s salt was inhibited by the presence of sulphate. Sulphate ion reacts preferentially with the calcium aluminate hydrates forming non-expansive ettringite which precipitated inside the pores; the microstructure was refined and the mechanical properties enhanced. This process was faster and more marked at 40°C. [Copyright &y& Elsevier]

This work is a continuation of a previous durability study of class C fly ash belite cement (FABC-2-W) in simulated radioactive liquid waste (SRLW) that is very rich in sulphate salts. The same experimental methodology was applied in the present case, but with a SRLW rich in sodium chloride. The study was carried out by testing the flexural strength of mortars immersed in simulated radioactive liquid waste that was rich in chloride (0.5M), and demineralised water as a reference, at 20 and 40°C over a period of 180 days. The reaction mechanism of chloride ions with the mortar was evaluated by scanning electron microscopy (SEM), porosity and pore-size distribution, and X-ray diffraction (XRD). The results showed that the FABC mortar was stable against simulated chloride radioactive liquid waste (SCRLW) attack at the two chosen temperatures. The enhancement of mechanical properties was a result of the formation of non-expansive Friedel''s salt inside the pores; accordingly, the microstructure was refined. [Copyright &y& Elsevier]

Accurate and precise electron microscopic analysis of the remnant solid precursor (fly ash and blast furnace slag) particles embedded in an inorganic polymer cement (or “fly ash geopolymer”) provides critical information regarding the process of gel binder formation. Differential solubility of phases in the fly ash is seen to be important, with insoluble mullite crystals becoming exposed by the retreat of the surrounding glassy phases. High-iron particles appear to remain largely unreacted, and the use of sectioned and polished specimens provides a view of the inside of these particles, which can show a wide variety of phase separation morphologies and degrees of intermixing of high iron and other phases. Calcium appears to be active in the process of alkali activation of ash/slag blends, although the competitive and/or synergistic effects of ash and slag particles during the reaction process remain to be understood in detail. [ABSTRACT FROM AUTHOR]

By scanning electron microscopy and microanalysis of fly ash-based and mixed fly ash-slag inorganic polymer cement (i.e., “fly ash geopolymer”) binders, a more detailed understanding of the gel structure and its formation mechanism have been developed. The binder is predominantly an aluminosilicate gel charge balanced by alkali metal cations, although it appears that calcium supplied by slag particles becomes relatively well dispersed throughout the gel. The gel itself is comprised of colloidal-sized, globular units closely bonded together at their surfaces. The microstructure of the binder resulting from hydroxide activation of fly ash is much less uniform than that which forms in a corresponding silicate-activated system; this can be rationalized in terms of a newly developed explanation for the differences in reaction mechanisms between these two systems. In hydroxide activation, the newly formed gel phase nucleates and grows outwards from the ash particle surfaces, whereas the high silica concentration in a silicate-activated system enables a more homogeneous gelation process to take place throughout the inter-particle volume. [ABSTRACT FROM AUTHOR]

To assess the effectiveness of the injected activated carbon, cement, and sulfur-containing chelating agent in controlling polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) release from the surface of air pollution control (APC) residues, this study examined the leachability of PCDD/Fs from APC residues generated by municipal solid waste incinerators. Results showed that PCDD/Fs were stably retained in the APC residues when the samples were leached with acetic acid solution. Highly chlorinated PCDD/F homologues (i.e., hepta- and octa-CDDs and CDFs) were relatively easy to leach. The leaching percentages of PCDD/Fs from raw APC residue samples containing activated carbon were smaller than those from samples without activated carbon, especially when n-hexane was used as the leachant. These results indicate that the flue gas injected activated carbon not only controls PCDD/F emissions, but also suppresses the leachability of PCDD/Fs from the APC residues. Solidification/stabilization (S/S) processes with 30wt% cement and 5wt% sulfur-containing agent can additionally decrease the leachability of PCDD/Fs with humic acid. Using n-hexane as the leachant, S/S processes increased the leachability of PCDD/Fs. Various low chlorinated PCDD/F congeners were moreover leached out of the APC residue samples, markedly increasing the leachate toxicity. The enhancement of leachability and toxicity owing to S/S processes may negatively impact the environment when APC residues are exposed to nonpolar organic solvents. [Copyright &y& Elsevier]

The article presents a study on determining the conditions of accelerated carbonation of reactive magnesium oxide (MgO) cements. The cements are blends of MgO, portland cement and pulverized fuel ash. It presents the exposure of samples to two levels of carbon dioxide at two levels of relative humidity (RH). Results showed that the carbonation of MgO yields nesquehonite and revealed that accelerated carbonation treatment can damaged the blends in the absence of MgO.