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The performance of green mortars (GMs) incorporating an eco-cement made from various proportions of rice husk ash (RHA), ground granulated blast-furnace slag (GGBFS) and circulating fluidised bed combustion fly ash (CFA) was evaluated. Different RHA contents (15 wt%, 30 wt% and 45 wt%) were used to replace GGBFS (by weight) and these mixtures were activated by 15 wt%, 20 wt% and 25 wt% CFA by the total weight of GGBFS and RHA. The engineering properties of the mortars were examined by compressive strength, splitting tensile strength, water absorption, porosity and dynamic Young's modulus tests. Sulfate resistance tests and scanning electron microscopy (SEM) were conducted to evaluate the durability and microstructure of the GMs. The test results demonstrated that the content of RHA and CFA strongly impacted the properties of the GMs. The mortars with 20 wt% CFA and

This research investigated the effects of recycled fine aggregate (RFA) and fly ash (FA) content on the strength development and engineering properties of alkali-activated slag–MgO (AASM) mortar. Various mortar specimens in which natural sand was replaced by RFA in five ratios (0:100, 25:75, 50:50, 75:25, and 100:0) and 0%, 15%, 30%, and 45% of the slag content was replaced by FA were prepared. Finally, the MgO content was fixed at a constant 7.5% of slag and FA by weight. These mixtures were activated using a solution of sodium hydroxide and sodium silicate. Strength and engineering properties, including flowability, unit weight, water absorption, ultrasonic pulse velocity (UPV), electrical surface resistivity (ESR), and rapid chloride penetration test (RCPT), were evaluated for all of the mortar samples throughout 56 days of curing time. The findings demonstrate that RFA and FA contents significantly affected the properties of mortar specimens, with RFA negatively influencing these properties and the 15% FA content specimen showing the most significant improved strength and engineering properties. Moreover, all of the AASM mortar mixtures exhibited good strength and high durability, with high UPV and ESR values as well as low-RCPT results.

This study investigates the manufacture and engineering properties of cementitious mortar incorporating unground rice husk ash (URHA) as fine aggregate. Six mixtures of mortar were produced...

Brick and ceramic wastes are becoming one of the most abundantly generated construction and demolition waste (CDWs). However, the practice of utilizing high volume brick and ceramic waste as a precursor and fine aggregate materials in alkali-activated mortar has not yet been exhaustively studied. The main purpose of this research was to analyze the possibility of recycling brick and ceramic wastes as a precursor and fine aggregate in high volume basis in the development of alkali-activated brick and ceramic mortar (AABCM) under ambient temperature. In this respect, waste brick powder (WBP) and waste ceramic sand (WCS) were used as a precursor and fine aggregate, respectively, and ground granulated blast furnace slag (GGBFS) was used to replace WBP in a range of 0–50% at increments of 10% by volume. The AABCM samples were prepared and cured at an ambient temperature for 3, 7, 28, and 56 days: the compressive strength measured in the range of 24–93 MPa and ultrasonic pulse velocity (UPV) values were between 3112 and 4086 m/s indicating AABCM samples were in good condition; both showed improvement when the proportion of GGBFS was increased. The results of this study reveal the strong potential of using brick and ceramics as precursor and fine aggregate materials on a high-volume basis to produce AABCM under ambient temperature conditions.

The main purpose of this study was to develop a high-strength alkali-activated paste using a high volume of waste red clay brick powder (WBP) and waste ceramic powder (WCP) as source materials. The reference mixes in this study were prepared using 100% WBP and 100% WCP. In the trial mixes, the WBP and WCP comprised about 60% of the total weight of the starting materials, while fly ash (FA) and ground granulated blast furnace slag (GGBFS) comprised the remaining 40%. Increments of the latter in the different trial mixes varied from 10% to 30% of the total weight. A solution of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) was used as the alkali activator. Alkali-activated paste (AAP) samples were prepared and cured at ambient temperature for 3, 7, 28, and 56 days. Workability, compressive strength, ultrasonic pulse velocity, thermal conductivity, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses were conducted in order to study the engineering and microstructure performance of these samples. The test results revealed that the fresh AAP mixtures were highly workable with measured slump flow values of 235–300 mm. Moreover, the hardened AAP samples obtained high compressive strength results measured in the range of 36–70 MPa. The AAP samples with WBP showed better mechanical strength performance and denser morphology than those with WCP. It is attributable to the enhancement of alkali activation of the AAP due to the finer particle size and higher CaO content of the WBP as compared to the WCP. The results of this study further demonstrate the strong potential of using recycled WBP and WCP in the production of high-strength AAP.

The present study aims to investigate the performance of alkali-activated fine slag under water curing condition. Ground granulated blast furnace slag (GGBFS) with a fineness of 6000 cm2/g was alkali-activated by the premixed alkaline solution from sodium hydroxide and sodium silicate liquid with the constant Na 2 O concentration at 5% and the modulus ratio of SiO 2 /Na 2 O at 0.5. Water-to-solid (w/s) ratio varied from 0.3, 0.4 and 0.5 to examine the effect of w/s ratio on the strength development and cracking performance of the AAS specimens. The compressive strength test, crack observation, and thermal conductivity test were conducted. The compressive strength results showed that this property was adversely affected by the w/s ratio, and the strength slowly increased after 7 curing days. Macro-cracks occurred in water-cured AAS cubes and they were more server in the specimens with lower w/s ratio. Besides, as the w/s ratio decreased, these AAS performed higher thermal conductivity.

This research investigated the feasibility of utilization of mine tailing, a disposal from mining exploitation process, to produce the cement mortar samples. Based on Densified Mixture Design Algorithm (DMDA) method, the mix-proportions in which fly ash (FA) accounted for 5% by total weight of FA and mine tailing were carried out on varied water-to-binder (w/b) ratios of 0.3, 0.4, and 0.5. Compressive strength, ultrasonic pulse velocity (UPV) and thermal conductivity tests were examined the engineering performance of mortar specimens. All mine tailing mortar specimens performed exceptional engineering properties, which were greatly affected by w/b ratio. The greatest compressive strength obtained in this study were 70.4 MPa in the mortar with w/b of 0.3. Increasing the w/b ratio had a negative impact on strength, UPV and thermal conductivity of mortar specimens.

This study investigated the engineering properties and durability of high-performance recycled aggregate concrete (HPRAC) specimens. The specimens were prepared using alkali-activated slag ...

The present study investigates the effect of magnesium oxide (MgO) on the respective performance of water- and air-cured alkali-activated fine slag (AAS). Ground granulated blast furnace slag (GGBFS) of two different fineness levels were used to produce two AAS mixtures. These mixtures were alkali-activated with sodium hydroxide and sodium silicate and prepared into samples by adding, respectively, 2.5%, 5%, 7.5%, 10% and 15% MgO by total binder weight. A series of tests, including slump flow, setting time, compressive strength, X-ray diffraction (XRD), scanning electronic microscopy (SEM) and thermogravimetric analysis were conducted in accordance with the relevant standards. In terms of findings, the addition of MgO promoted the hydration of AAS significantly at early curing ages. Optimum MgO content was 7.5% for slag-4000 specimens and 5% for slag-6000 specimens. Cracks were observed in the water-cured AAS samples, with greater cracking at higher levels of MgO content. Moreover, the results show that the main contribution of MgO is in the hydrotalcite-like phase (Ht), where it adds volume, which improves strength the AAS paste. The effect of MgO was significantly increased in the samples that used finer-particle GGBFS. Adding MgO contributed to the more formation of hydration products, which was observed in the present study using X-ray diffraction and SEM and derivative thermogravimetric analysis.

This paper presents the results of the experimental works to investigate the use of waste limestone from water treatment industry as fine aggregate in green concrete. Two concrete mixtures with a constant water-to-binder ratio of 0.3 were prepared for this investigation, in which, the normal concrete mixture was designed following the guidelines of ACI 211 standard, while the green concrete mixture was designed using densified mixture design algorithm (DMDA) technology. For comparison, both types of concrete samples were subjected to the same test program, including fresh properties, compressive strength, strength efficiency of cement, drying shrinkage, electrical surface resistivity, ultrasonic pulse velocity, and thermal conductivity. Test results indicate that both concrete mixtures showed the excellent workability due to the round-shape of waste limestone aggregate and the use of superplasticizer. In addition, the green concrete mixture exhibited a better performance in terms of engineering properties and durability in comparison with the normal concrete mixture. The results of the present study further support the recycling and reuse of waste limestone as fine aggregate in the production of green concrete.

This paper investigates both fresh and hardened properties of concrete produced with different particle sizes of coarse aggregate (CA). The CAs with the maximum sizes (Dmax) of 25 mm, 19 mm, 15 mm, 12.5 mm, and 9.5 mm were used to produce concrete samples with a water-to-binder ratio of 0.4. The workability, fresh unit weight, compressive strength, and ultrasonic pulse velocity (UPV) of the concrete were tested. Additionally, some concrete samples were fully immersed in 5% sodium sulfate solution in order to assess the performance of the concrete under sulfate attack condition. The experimental results show that the workability of fresh concrete increased with increasing the particle size of CA used, while the particle size of CA insignificantly affected to the unit weight of fresh concrete mixtures. The concrete mixture produced with Dmax of 12.5 mm obtained the highest compressive strength and UPV values in comparison with those of other mixtures. This study also found that the compressive strength values of concrete samples that fully immersed in sulfate solution reduced about 15% as compared with those of the concrete samples cured in lime-saturated water. All of the concrete samples prepared for this investigation exhibited good durability performance with ultrasonic pulse velocity values of above 4300 m/s. Test results also indicated that the concrete properties can be enhanced if the CA sizes were appropriately selected.

The present study evaluates the mechanical-microstructural characteristics of the densified high-performance concrete (HPC) incorporating high volume fly ash (FA). The densified mixture design algorithm (DMDA) technology was applied to design the concrete proportions. The effects of various FA contents on both fresh and hardened concrete were investigated. A scanning electron microscope (SEM) was used to observe the microstructure of the concrete samples. The effectiveness of using DMDA in mix deign was also discussed in this study. As the experimental results, the FA content was found to affect the concrete properties significantly. The maximum compressive strength value of 65.1 MPa was obtained at the concrete samples containing 40% FA. Additionally, the 40% FA samples exhibited a denser microstructure as compared to the others. Generally, all of the tested concrete samples exhibited good performance in terms of workability, strength development, water absorption, and porosity. The results of this study further show the effectiveness of using DMDA technology in proportioning of the concrete mixture.

Creep and shrinkage behaviors are critical factors in the precast/prestressed concrete industry because these factors allow engineers to assess the long-term performance of concrete and to develop life-cycle estimates for concrete structures. The current study presents the results of an experimental work that addresses creep and shrinkage behaviors as well as the development of compressive strength in ordinary Portland cement concrete (OPC), high-performance concrete (HPC), and self-consolidating concrete (SCC). The concrete mixtures created for the present study were used to fabricate prestressed bridge girders. A conventional method (ACI) was used to design the mixture proportion for OPC and a densified mixture design algorithm (DMDA) was used to design the mixture proportions for HPC and SCC. All concrete mixtures had the same target strength of 69 MPa (10000 psi) at 56 days. Additionally, a comparative performance in terms of strength development and creep and shrinkage behaviors of ACI and DMDA concrete is performed in the present study. Test results show that all of the samples attained the target strength after 28 days of curing and that the strengths of each continued to increase afterward. Importantly, the incorporation of pozzolanic materials into concrete mixtures affected the propagation of creep strain and shrinkage positively. Furthermore, the DMDA concrete sample delivered better long-term performance than ACI concrete in terms of compressive strength, creep strain, and shrinkage.

This study used a sodium hydroxide (NaOH) solution to activate a mixture of water treatment sludge, fly ash, and slag, in order to produce a new alkali-activated controlled low-strength material (CLSM). Fresh properties of this new CLSM were investigated through the tests of workability, setting time, and ball drop time. Test results show that the addition of water treatment sludge (WTS) decreased workability. In addition, the addition of such WTS increased initial setting time and ball drop time, whereas the alkali equivalent (AE) shortened the initial setting time and ball drop time. At a liquid-to-solid ratio (L/S) of 0.9, a WTS content of 10%, and an alkali equivalent of 9%, the fresh properties for the CLSM conforms to the design principles and provisions of the Public Works Department, Taipei City Government, and is ideal for road construction in order to reduce traffic impact.

Thin-film transistor liquid-crystal display (TFT-LCD) waste glass can be used as a raw material for producing geopolymers, because it contains large amounts of silicon and aluminum in its amorphous structure. The setting time and compressive strength were evaluated to determine the quality of the geopolymer product with various amounts of nano-SiO2 (0% 3%) and TFT-LCD waste glass replacement (0% - 40%). The microstructures of the samples were characterized using mercury intrusion porosimetry (MIP), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The highest compressive strength and compact microstructure of the geopolymer was attained by adding 10% waste glass and 1% nano-SiO2. The results demonstrated that adding nano-SiO2 to the geopolymer substantially enhances compactness, improves uniformity, and greatly increases compressive strength. This work offers a low-cost route for fabricating geopolymers, because TFT-LCD waste glass can be used to partially substitute metakaolin in the composition of the geopolymer.

The present study evaluates the engineering properties and durability of an eco-friendly mortar that was produced using an innovative cement-free SRF binder. Samples of the binder, which incorporated ground granulated blast furnace slag (GGBFS) (S), rice husk ash (RHA) (R), and circulating fluidized bed combustion fly ash (CFBC) (F), were prepared for the present study using four different RHA/GGBFS weight ratios (0/100, 15/85, 30/70, and 45/55) and three different amounts of CFBC (10%, 20%, and 30%) as an activator. The properties of the mortar samples were evaluated using compressive strength, water absorption and porosity, ultrasonic pulse velocity (UPV), electrical surface resistivity (ESR), and sulfate resistance. The effects of RHA and CFBC contents on the properties of the mortar samples were studied. Test results showed that both the RHA and CFBC affected the properties of the mortar samples significantly. At later curing ages, the mortar samples that incorporated 20% CFBC and 30% RHA exhibited the highest compressive strength values. Furthermore, all of the cement-free mortar samples exhibited good durability, as indicated by high UPV and ESR values and high resistance to sulfate attack.

This study investigated the performance of cement-free binders incorporating ground granulated blast furnace slag (GGBFS), rice husk ash (RHA), and circulating fluidized bed combustion fly ash (CFA). Changes in packing density, water absorption, porosity, chloride penetration, and their correlations were evaluated in specimens produced using four different RHA/(RHA + GGBFS) weight ratios (0%, 15%, 30%, and 45%) and three different CFA/(RHA + GGBFS) weight ratios (10%, 20%, and 30%). The results indicate that changes in RHA and CFA proportions affected binder properties significantly. Furthermore, the high resistance to chloride penetration in the specimens support that these binders provide good durability.

The present study aims to investigate the engineering properties of foam lightweight material (FLM) that was produced using a mixture of ordinary Portland cement (OPC) and limestone powder (LP). The FLM samples were prepared with various proportions of LP (10%, 20%, and 30%) and different percentages of foam (9%, 12%, and 15%). Properties of the FLM were evaluated through the values of compressive strength, dry density, porosity, and thermal conductivity. Test results show that the foam contents affected all properties of the FLM significantly, whereas LP contents showed the insignificant effect to the FLM properties. Furthermore, the results of the present study showed a close correlation between porosity and other properties of the FLM as higher porosity resulted in lower density and thus lower thermal conductivity and mechanical strength.

The feasibility of recycling the reduction slag, limestone sludge, iron-oxide sludge, and stone sludge produced in the manufacture of cement was investigated through compressive strength testing, differential thermal and thermogravimetric analysis, X-ray diffraction, and 29Si nuclear magnetic resonance analysis. The major crystalline phases of ecocement clinkers, namely C3S, β-C2S, C4AF, and C3A, were observed. C3S content decreased and β-C2S and α-C2S content increased in the reduction slag. The compressive strength of EcoA pastes (ecocement contain 78% of limestone sludge, 19.51% of stone sludge and 2.49% iron-oxide sludge) was similar to that of commercial ordinary Portland cement. The Q0 (−70 ppm) species shifted to the Q1 (−80 ppm), and Q2 (−87 ppm) species during curing. The addition of stone sludge, iron-oxide sludge, and limestone sludge had no negative effect on the hydration of the cement pastes. In contrast, the addition of reduction slag negatively affected the formation of clinker minerals. Cement samples with reduction slag content of 1–7 wt % had lower 28-, 60-, and 90-day compressive strength than did the control mix. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 669–677, 2018

This investigation evaluates the characteristics of alkali-activated controlled low-strength materials (CLSM) that were produced using a mixture of red mud (RM) and ground granulated blast-furnace slag (GGBFS) with different RM-to-GGBFS weight ratios (100/0, 90/10, 80/20, and 70/30). A sodium hydroxide (NaOH) solution of 5M concentration was used as an activator. Characteristics of raw materials were checked carefully before using. The effects of GGBFS content on both fresh and hardened properties of the CLSM were evaluated through the tests of flowability, setting time, and compressive strength. Additionally, a scanning electron microscope (SEM) was used to examine the microstructural properties of the CLSM. Experimental results show that using more GGBFS in the mixture reduces flowability and increases the compressive strength of the CLSM. Moreover, the setting time of the fresh CLSM is associated positively with GGBFS content. Further, analysis of the optimal mixture was conducted basing on the test results. Thus, the properties of the CLSM sample containing 80% RM and 20% GGBFS conformed well to the requirements of the Public Works Department, Taipei Government, Taiwan. The results of this study further support the potential use of RM-GGBFS blends for the production of alkali-activated CLSM.

Waste materials have traditionally been discarded in landfills and often dumped directly into ecosystems without adequate treatment. However, possible reuse and recycling alternatives should be investigated and implemented. Recent environmentally friendly approaches have been aimed at achieving sustainable development by conserving natural resources and minimizing the discarding of materials. The objective of the present study was to investigate the hydration characteristics of reduction slag, limestone sludge, stone sludge, and iron-oxide sludge for fabricating four types of eco-cement clinkers. The compound raw materials were burned for 2 h at 1400°C to form eco-cement clinkers. The results showed that the major components of ordinary Portland cement (OPC), namely C3S, C2S, C3A, and C4AF, were present in the eco-cement clinkers. The compressive strength development of EcoA pastes (containing 78% limestone sludge, 19.51% stone sludge, and 2.49% iron-oxide sludge) was similar to that of the commercial OPC products. The compressive strength of the EcoD pastes (containing 71% limestone sludge, 19.51% stone sludge, 2.49% iron-oxide sludge, and 7% reduction slag) decreased as the amount of α-C2S increased. Mercury intrusion porosimetry indicated that the pore volume of the pastes gradually decreased with an increase in the curing time. Furthermore, the results of physical-mechanical tests showed that reduction slag, limestone sludge, stone sludge, and iron-oxide sludge can be used as raw materials in cement production at no cost to the producer, thereby reducing the production costs. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1466–1473, 2017

Controlled low-strength material (CLSM) is a self-compacting, flowable, and low-strength construction material that is used widely in variety construction applications. The present study evaluates the properties of CLSM that was prepared using a mixture of class-F fly ash (FA) and ground granulated blast-furnace slag (GGBFS) with the addition of three different ratios (0%, 10%, and 20% as calculated by combined FA and GGBFS weight) of waste water treatment sludge (WTS). A sodium hydroxide (NaOH) solution was used to activate these powder materials in the mixture in order to produce the alkali-activated CLSM. The effects of adding WTS on the properties of both fresh and hardened CLSM are evaluated using workability, setting time, drop ball time, unit weight, compressive strength, and toxicity characteristic leaching procedure (TCLP) tests. Moreover, a scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) is used to examine the microstructural properties of the CLSM. Results show that adding WTS to the CLSM samples reduces workability and increases fresh unit weight and compressive strength. Additionally, initial setting time and drop ball time are both associated positively with level of WTS content. Moreover, the liquid-to-solid (L/S) ratio and the alkali equivalent (AE) are shown to affect the properties of the CLSM significantly. The TCLP assessed leaching concentrations of heavy metals are all significantly below the regulatory thresholds that are currently allowed by the Environmental Protection Administration (EPA) in Taiwan. Finally, the properties of the CLSM sample with an L/S ratio of 0.9, WTS of 10%, and AE of 9% are found to conform well to the requirements of the Public Works Department, Taipei Government in terms of design principles and provisions.

This study aims to investigate engineering properties of cementless pastes which were produced by reactive magnesium oxide (MgO) and ground granulated blast furnace slag (GGBFS). The mixtures were designed in various levels of MgO at 2.5%, 5%, 7.5%, 10%, 15% and 20% of total binder weight. The slump flow test, compressive strength test, ultrasonic pulse velocity test (UPV) and thermal conductivity test were conducted to examine the engineering properties of the pastes until 28 curing days. The results indicate that the high proportion of MgO causes the decrease of flow-ability of fresh pastes. Increasing MgO content significantly promotes the hydration process and improves the compressive strength and hardened properties of pastes through the UPV and thermal conductivity testing results.

The aim of this study was to reuse recycled concrete aggregates for concrete production by using the Densified Mixture Design Algorithm (DMDA) method for blended aggregates and mixing design based on the evaluation of characteristics of recycled aggregate concrete (RAC). Recycled coarse aggregate (RCA) was used to replace 30%, 40%, and 50% of the natural coarse aggregate (NCA), respectively, by volume in the samples, and the fine aggregate was a combination of 70% natural fine aggregate (NFA) and 30% recycled fine aggregate (RFA) by volume. A series of tests, including compressive strength, splitting tensile strength, ultrasonic pulse velocity (UPV), electrical surface resistivity (ESR), thermal conductivity (TC), water absorption, and the rapid chloride penetration test (RCPT) were conducted in accordance with the relevant standards. The results illustrated that blending aggregates following to DMDA method suggested an optimum proportion of RCA level which exhibited with highest volume of aggregate per unit volume of combination of RCA and NCA. The results revealed 40% RCA content as the optimum replacement level. Furthermore, the 40% RCA concrete mix exhibited good hardening properties in terms of being only slightly below the 30% RCA mix and significantly higher than the 50% RCA mix. All of the RAC mixtures designed by DMDA method with low cement consumption exhibited good strength development and good durability through 120 days of curing.

The present study examines the effect of adding random, short coconut fibers to various cementitious composites on the mechanical properties, plastic cracking, and impact resistance of these composites. Fibers underwent a washing and boiling pretreatment prior to being added to the composite mixture. Mixtures of the cementitious composites designed by Densified Mixture Design Algorithm (DMDA) method were made using different volume fractions of random, short coconut fiber (0%, 1%, 2.5%, and 4%) and different water-to-binder (W/B) ratios (0.3, 0.35, and 0.45). Furthermore, fly ash (FA) was used to fill the void between sand particles and ground blast furnace slag (GBFS) was used to substitute for the cement in the mix proportions. A variety of tests were conducted in accordance with the relevant standards to determine the properties of these coconut fiber cementitious composites. The findings show that higher volumes of coconut fiber in the mortar tend to reduce the density and to increase the superplasticizer dosage. The addition of coconut fiber and higher W/B ratios were associated with lower compressive strength and higher absorption. The 28-day flexural strength of cementitious sheets and the modulus of rupture, respectively, increased from 5.2 to 7.4 MPa and from 6.8 to 8.8 MPa, as the coconut-fiber-to-mortar ratio ranged from 0% to 4%. Adding coconut fiber positively influenced first-crack deflection, toughness indices, plastic cracking, and impact resistance in the composites.

This article presents the results of a study on the effects of solid-to-liquid (S/L) ratio and of curing temperature on strength development, phase composition, and microstructure in geopolymers that prepared using a mixture of class-F fly ash (FA) and residual rice husk ash (RHA) and a solution of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). The samples were prepared at various S/L ratios (2.4–2.8) and then cured at various curing temperatures [room temperature (RT): 90°C] to investigate these effects. A compressive strength test was conducted on the samples after the curing process to determine the development of strength over time. Moreover, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to examine the microstructural properties of the samples. Furthermore, scanning electron microscopy was used to characterize the surface morphologies of the samples. This study found that the S/L ratio and the curing temperature had significant effects on the properties of the geopolymer samples. The compressive strength of all the geopolymer samples increased with curing age. The highest strength was obtained from the samples that were prepared at an S/L ratio of 2.6 and a curing temperature of 60°C. XRD and FTIR analyses showed that the major crystalline phases presented in the resultant samples were quartz, mullite, and cristobalite with the additional presence of minor zeolite phases. The results of this study support the use of FA and RHA as solid waste materials in the preparation of geopolymers. © 2016 American Institute of Chemical Engineers Environ Prog, 2016

The present study investigates the possibility of using a blended class-F fly ash (FA) and residual rice husk ash (RHA) in the production of green building bricks through the application of densified mixture design algorithm (DMDA) in order to provide a new use for solid waste materials. This study uses unground rice husk ash (URHA) as a partial fine aggregate substitution (10–40%) in the studied cementitious mixtures. Solid bricks of 220 × 105 × 60 mm in size were prepared under forming pressure of 25–35 MPa, a curing temperature of 90 °C, and a relative humidity of 50%, for tests that assessed: compressive strength, flexural strength, bulk density, void volume, and water absorption. The test results showed that all brick samples demonstrated excellent properties. Compressive strength and flexural strength ranged, respectively, between 20.2–33 MPa and 5.4–6.9 MPa. Additionally, up to 30% of URHA content, the values of water absorption and void volume ranged, respectively, between 8.8–15.7% and 1....

This study was designed to examine the mechanical properties and durability of high-performance recycled aggregate concrete (HPRAC) containing high percentages of construction and demolition waste (CDW). In the samples, natural coarse aggregate was replaced with recycled coarse aggregate at respective ratios of 30%, 40%, and 50%, and natural fine aggregate was replaced with recycled fine aggregate at respective ratios of 40% and 50%. The concrete mixtures were designed using the Densified Mixture Design Algorithm (DMDA) method with low cement content and water binder (w/b) ratios of 0.3, 0.4, and 0.5. Concrete samples were tested for compressive strength, splitting tensile strength, ultrasonic pulse velocity (UPV), electrical surface resistivity (ESR), thermal conductivity (TC), water absorption (WA), and rapid chloride penetration and were analyzed using scanning electron microscope (SEM) micrographs for microstructure. The results support a negative relationship in concrete between CDW content and strength and durability development as well as between the w/b ratio and mechanical properties and durability. However, all of the HPRAC specimens designed in this study using the DMDA method achieved a high strength range, good durability, and stability over curing time.

This paper investigates the effects of adding magnesium oxide (MgO) on the engineering properties and microstructure of alkali-activated slag (AAS)-rice husk ash (RHA) paste that has been produced using an aqueous mixture of sodium hydroxide and sodium silicate as the crucial activator. Three percentages (20%, 30% and 40%) of RHA as partial replacement of slag and four percentages (2.5%, 5%, 7.5% and 10%) of MgO in the binary mixture of slag and RHA were used to manufacture the MgO-modified, alkali-activated slag-RHA mixture (AASR). These mixtures were then compared with the reference AAS, which was manufactured without RHA and MgO. Experimental results showed that the higher RHA and MgO levels caused a negative effect on the workability of AASR fresh samples. The 20% RHA percentage samples exhibited the best engineering properties of all of the samples and superior engineering properties to the reference AAS. Moreover, adding 7.5% MgO significantly improved the mechanical properties and thermal conductivity of the AASR paste samples. Finally, microstructural examination using X-ray diffraction (XRD), scanning electronic microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) identified hydrotalcite-like phase (Ht), C–S–H as the primary hydration products of the MgO-modified AASR, included with cristobalite, and un-hydrated MgO.

This study combines various proportions of class-F fly ash (FA) and residual rice husk ash (RHA) with an alkaline solution to produce geopolymers. All of the geopolymer samples were cured at 35 °C and at 50% relative humidity until the required testing ages. The effects of the RHA content (0–50%) and of the concentration of the sodium hydroxide (NaOH) solution (8–14 M) on the compressive strength development of the samples were then investigated. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to examine the microstructural properties of the samples. Further, scanning electron microscopy (SEM) coupled with energy dispersive spectrometer (EDS) was used to characterize sample surface morphologies and compositions. Results found that the samples prepared with a NaOH concentration of 10 M and a RHA content of 35% exhibited the highest compressive strength and that increasing the NaOH concentration and RHA content beyond these values exhibited decreasing compressive strength. Chemical analysis showed that the major crystalline phases presented in the resultant geopolymer were quartz, mullite, and cristobalite. Furthermore, minor zeolite phases were detected in all of the geopolymer samples. The results of the present study support FA and RHA as promising solid waste materials for use in the production of geopolymers.

Geopolymers, which are a new form of aluminosilicates, are environmentally friendly materials that exhibit high mechanical strength. Waste catalysts that contain a large amount of amorphous SiO2 and Al2O3 are highly soluble in alkaline solutions. This study investigated the effects of the SiO2/Na2O ratio (S/N) and various levels of waste-catalyst replacement on the properties of waste-catalyst metakaolin-based geopolymers (WCMBGs). The mechanical and microstructural properties of the materials were studied by performing compressive strength testing, porosity analysis, thermogravimetric analysis, 29Si magic-angle spinning nuclear magnetic resonance (29Si MAX NMR) spectroscopy, and scanning electron microscopy. When S/N was 1.93, WCMBGs containing 10% of the waste catalyst exhibited high compressive strength and low porosity. Thermogravimetric analysis indicated that the weight loss of the materials was related to the structural composition. 29Si MAX NMR results showed that the major structure of the elements Si and Al was Q4(3Al). The experimental results indicated that waste catalyst can potentially serve as a partial replacement for metakaolin and exhibits favorable mechanic characteristics.

Using solid waste materials in the production of construction materials has received considerable attention across the world. The present study investigates the feasibility of using the densified mixture design algorithm (DMDA) method to incorporate unground rice husk ash (URHA) as a partial fine aggregate replacement (0–40%) in the production of eco-friendly construction bricks. Fly ash (FA) and residual rice husk ash (RHA) are the main binder materials considered in this study. Solid bricks of 220 × 105 × 60 mm in size were prepared in accordance with official Vietnamese product standards in steel molds under 35 MPa forming pressure. After casting, the brick samples were stored at 35 °C and a relative humidity of 50% until the ages required for testing. The brick samples were checked for dimensions and visible defects. The effects of URHA content on the engineering properties of the solid bricks, including compressive strength, flexural strength, water absorption, bulk density, and void volume, were also investigated. The test results showed that all brick samples exhibited good physical and mechanical properties. Compressive strength and flexural strength ranged, respectively, between 20.9–31.5 MPa and 5.7–6.7 MPa. All of these values were significantly better than the values required by the official Vietnamese standards. The results of this study demonstrate a significant potential for applying URHA in the production of eco-friendly construction bricks.