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The attractive properties of ye'elimite (C4A3$) are receiving particular attention in cement and repairing materials. The present paper aims to further explore the difference in hydration performance of different C4A3$ phases (o-C4A3$ and c-C4A3$) using the Ga-doping method. On this basis, C4A3-xGx$ specimens (noted as C4A3$, C4A2.3G0.7$, and C4A1.6G1.4$) were first synthesized and their hydration characteristics were systematically studied. Results showed that Ga-doping enhanced the hydration activity of ye'elimite. With increasing Ga3+ ions addition, the intensity of the initial peak gradually increased, but the duration of the induction period and the hydration heat development rate were gradually reduced. The conductivity and pore solution analysis also demonstrated a higher ion concentration precipitation at the early stage for cubic C4A1.6G1.4$ compared to pure C4A3$. The main hydration products of these specimens were AFt, AFm, and AH3 (gel). Moreover, the addition of Ga3+ ions improved the crystallinity of AFt and AFm with recorded a relatively higher decomposition temperature. Overall, this study demonstrated that the addition of Ga3+ ions can regulate the hydration characteristics of ye'elimite.

Transforming phosphogypsum (PG) to β-hemihydrate PG with cementitious properties at low calcination temperature is an effective method for large-scale utilization of by-product PG. Nevertheless, due to the poor water resistance of PG, its application and recycling rate is limited. This study aims to produce water-resistant β-hemihydrate synthetic gypsum (SG) with minimum cost and energy consumption, using calcined PG as the raw material. The effect of PG calcination temperature (100 °C, 140 °C, 180 °C, and 220 °C) on the properties of SG was evaluated, and it was found that 180 ºC calcination temperature was able to fully convert the PG to β-hemihydrate SG. Additionally, SG prepared using 180 ºC calcined PG exhibited the highest compressive strength (9.15 MPa). On the other hand, various contents of the mineral admixture, namely, GGBS (5 %, 10 %, 15 %, 20 %, and 25 %), were incorporated in SG to evaluate the viability of GGBS to improve the compressive strength and water resistance of SG. However, the results revealed that adding GGBS has little effect on the performance of SG. Especially, when 25 % GGBS was added, the compressive strength of SG was reduced by 66.3 %. Consequently, further investigation into how to enhance the effect of GGBS is required.

Heavy metal contamination is regarded as one of the most serious hazards to the environment and living organism. The scenario is exacerbating especially due to the continuous development. Therefore, the goal of this study is to examine the copper ion removal potential of a facile-fabricated foamed geopolymer sphere. The foamed geopolymer sphere is synthesized via direct moulding method, using locally available materials of fly ash and calcined kaolin as the starting materials. The foamed geopolymer sphere is beneficial in terms of the ease of use where it can be used in packed bed system directly and the retrieval process upon exhausted is much simpler. Due to the plentiful binding sites created by foaming of the geopolymer sphere, the copper ion removal efficiency increases from 47.5% to 92.8% and the removal capacity improves by six times. pH 5 is identified to be the best pH for copper ion removal utilizing the foamed geopolymer sphere. The maximum copper ion removal capacity found experimentally is 37.9 mg/g, which is satisfactory compared to the foamed geopolymer spheres prepared via suspension and solidification. Meanwhile, increasing the dosage of the foamed geopolymer sphere can increase the foamed geopolymer sphere’s removal ability when concerning high copper ion concentration. Pseudo second-order kinetic and Langmuir isotherm models are found to describe well the adsorption process.

The aim of this paper is to investigate the effect of carbonation on the microhardness and mechanical-related properties of carbonated and uncarbonated layers of cement pastes. The microhardness and mechanical property changes were examined 1 day after demolding and then 3, 7, 14, and 28 days with further CO2 and water curing. CO2 treatment yielded substantial impacts on the microstructure and densification of the surface layer of the paste by consuming calcium hydroxide and forming calcium carbonates. The maximum carbonation depth of 5 mm was recorded at 28 days, and the microhardness of the surface layer was significantly enhanced compared to the internal layer as well as uncarbonated paste samples. However, despite improved surface hardness, the overall compressive strength of carbonated sample was lower than that of water-cured samples, probably due to the non-preconditioning (to remove excess water for carbonation) of the carbonated samples and better hydration in the internal layer of the samples cured in water. In addition, the thin denser surface layer of the carbonated samples could decrease the cement hydration process. However, the denser and lower surface water absorption relation to CO2 treatment could facilitate long-term durability performance of concrete structures.

Construction and demolition activities generate numerous waste that could be reutilized as recycled aggregates. The replacement of natural aggregate with recycled aggregate generally has negative impact on the performance of conventional concrete. This impact is found to be less significant in self-compacting concrete (SCC), owing to the better quality of binder which modifies the interfacial transition zone and lesser amount of coarse aggregates used. Considering the wide sources of recycled aggregates such as concrete, bricks and blocks, few studies were conducted on comparing the performance of SCC incorporating different types of recycled aggregates. In addition, since SCC is more commonly used in high-rise buildings which may experience fire risks, it is important to ascertain the corresponding high temperature resistance. In this paper, three different types of recycled aggregates are considered, namely recycled concrete aggregate (RCA), recycled brick aggregate (RBA), and recycled concrete block aggregate (CBA). 100 % replacement is feasible for SCC-CBA and SCC-RCA because of the minor strength reductions. The results also showed that the RBA and CBA concretes outperformed the NA concrete at high temperature (400 °C and 600 °C). RBA is suggested to partially replace natural aggregate, since it gives inferior performance at room temperature, but it is more recommended to be used in high temperature environments.

This research proposes the use of a basalt textile-reinforced mortar (TRM) system as an overlay to strengthen brick masonry. A comparison of the strength performances, namely, the compressive strength, flexural bond strength, and shear bond strength, between unreinforced brick assembly and basalt TRM-reinforced brick assembly was made. The reinforced specimens exhibited improved strength performance, in particular, the flexural bond and shear bond strengths whereby more than a two-fold increase was observed. Additionally, the coefficient of variations in the compressive and flexural bond strength of brick assemblies was reduced when reinforced with the basalt TRM. [ABSTRACT FROM AUTHOR]

Foamed mortar with a density of 1300 kg/m3 was prepared. In the initial laboratory trials, water-to-cement (w/c) ratios ranging from 0.54 to 0.64 were tested to determine the optimal value for foamed mortar corresponding to the highest compressive strength without compromising its fresh state properties. With the obtained optimal w/c ratio of 0.56, two types of foamed mortar were prepared, namely cement-foamed mortar (CFM) and slag-foamed mortar (SFM, 50% cement was replaced by slag weight). Four different curing conditions were adopted for both types of foamed mortar to assess their compressive strength, ultrasonic pulse velocity (UPV) and thermal insulation performance. The test results indicated that utilizing 50% of slag as cement replacement in the production of foamed mortar improved the compressive strength, UPV and thermal insulation properties. Additionally, the initial water curing of seven days gained higher compressive strength and increased UPV values as compared to the air cured and natural weather curing samples. However, this positive effect was more pronounced in the case of compressive strength than in the UPV and thermal conductivity of foamed mortar. [ABSTRACT FROM AUTHOR]

This paper examines the possibility of using ground-granulated blast-furnace slag (GGBFS) as a partial replacement of filler in polymer grout. In this study, river sand was replaced by GGBFS at levels of 0 (control), 10, 20, and 30% by weight. The effects of five curing conditions on compressive strength at the ages of 7, 28, 90, 180, and 365 days were studied. Three specimens were used at each specific age and curing condition. After 1 year, the samples' microstructures, which were cured under natural weather and seawater, were studied using scanning electronic microscopy (SEM). A comparison was also made regarding the development of compressive strength between polyester grout with and without GGBFS. From the results, it was observed that GGBFS used as filler in the polyester grout matrix resulted in a better long-term compressive strength than that of the control resin. The positive effects of GGBFS on the compressive strength of polyester grout against Malaysia's hostile environment, along with its environmental and economic advantages, make this material a feasible additive. [ABSTRACT FROM AUTHOR]