Conventional supplementary cementitious materials would decrease the alkalinity of pore solution, which is not beneficial for the stabilization of passive film on the surface of steel bars in the ...marine environment. By leverage of the alkali-rich and pozzolanic characteristics, this study first valorized waste glass powder (GP) to enhance the corrosion resistance of recycled aggregate concrete (RAC). The results showed that partially replacing cement with GP could improve the steel corrosion resistance of RAC to a level better than conventional concrete prepared with natural aggregates. Moreover, the presence of 20% GP significantly enhanced the chloride penetration resistance at a later age without sacrificing the compressive strength. The enhanced corrosion resistance of GP-RAC was attributed to two main reasons: i) the refined pore structure by the formation of secondary C-(N)-S-H gels with a lower Ca/Si ratio; ii) the increased alkalinity of pore solution due to the depolymerization of GP and the released Na+ from GP. As a result, the use of GP in low-carbon cement was able to compensate for the inferior durability of RAC. The proposed corrosion-resistant concrete with low ecological and economic costs has a promising application potential to promote the wider use of GP and RAC in the construction sector.
Abstract
The self-made polycarboxylic acid water reducer was used as a dispersant to investigate its influence on the dispersion property of new functional material graphene slurry. The dispersion ...technology in the preparation process of new functional material and the influence of the dosage of new functional material on the performance of concrete were studied. The results showed that the self-made polycarboxylic acid water reducer as a dispersant can improve the dispersibility of the new functional material graphene in water. When the ultrasonic dispersion time is 40min, it can be used to discharge bubbles in the graphene dispersion solution and improve the strength of concrete. By means of manual mixing, the concrete containing the dispersible liquid of the new functional material has less slump and less expansion loss at 1h, and higher compressive strength at 3 d, 7 d, and 28 d. The 7 d and 28 d compressive strength of concrete can be significantly improved when the content of new functional material graphene dispersion is 0 ∼ 0.23 %, and the optimal content of graphene dispersion is 0.05 %.
This work aims to improve heat resistance and mechanical properties of PEEK composites by filling the modified phosphates with inorganic particles (Si3N4, AlN, Al2O3 and Cu2O) as reinforcements. The ...modified phosphate/PEEK composites were successfully prepared by pre-mixing and compression molding. The crystalline structures and compositions of modified phosphates and composites are characterized. Furthermore, the thermal and mechanical properties of composites were evaluated by thermal aging resistance at 350 °C for 24 h. The results show that all the four kinds of phosphate reinforcements can enhance the thermal aging resistance of phosphate/PEEK composites to varied extent. For the modified phosphate by Al2O3, its addition increases the 30% weight loss temperature (T30) by 55 °C. Moreover, the compressive strength exhibits a 105.6% enhancement, reaching 321.4 MPa from 156.3 MPa of the PEEK matrix. This work provides a valuable route to improve the thermal and mechanical properties of PEEK composites, which would have promise applications in heat-resistant and high-strength structural materials.
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•Phosphates modified by Si3N4, AlN, Al2O3 and Cu2O particles were used as the reinforcement of PEEK composites.•Modified phosphate/PEEK composites could be prepared by molding and thermal treating at 350 °C.•Modified phosphates have a sufficient impact of the thermal and mechanical properties of PEEK composites.•T30 could be increased by about 55 °C, and the compressive strength was increased by 105.6%.
This paper intends to develop geopolymer-based composites for geothermal energy applications. Both silicon carbide (SiC) sand and SiC powder were applied to optimize the thermal and mechanical ...behaviours of geopolymer. The flexural and compressive strength of geopolymer composites with different mix designs were investigated. A novel test set-up to record the thermal conductivity were designed, and the thermal behaviours of geopolymer composites with different mix design were tested. It was found that the proper addition of SiC powder is conducive to the compressive and flexural strength of geopolymer composites, while the influence of SiC particles is insignificant. The relationship between flexural and compressive strength of geopolymer composites was also investigated, and it was found that the Portland cement association (PCA) code reached the best fitting precision. With the addition of SiC materials, the maximum thermal conductibility of geopolymeric composite can be as high as 5.35 Wm−1K−1, which is about five times higher than conventional cementitious composite. The combined application of SiC powder and SiC particle is practical to increase the thermal conductivity of geopolymer, making it a suitable material for geothermal energy applications. Based on the numerical model, it was concluded that the addition of silicon carbide is beneficial to the heat exchange rate of the energy pile and improves the heat utilization efficiency of the energy pile.
This study presents a one-part blend using ground granulated blast furnace slag (GGBFS) as the primary aluminosilicate precursor, with silica fume (SF) as an additive, activated by an equivalent NaOH ...achieved by balancing powdered industrial-grade soda ash (SA) and hydrated lime (HL). Conventional concreting methods are used, with mix design proposed using the packing density approach. Taguchi-Grey Relational Analysis optimizes control factors, including equivalent NaOH content, SF amount, water-to-solid ratio (w/s), and excess paste content. The study investigates their effects on fresh concrete properties like setting time, compactibility, and mobility, as well as hardened concrete properties like compressive strength and sorptivity. Findings reveal that setting time is mainly influenced by the w/s ratio, compactibility improves with higher equivalent NaOH content, and excess paste content affects particle friction. Initial strength gain is influenced by equivalent NaOH content, while later-age strength development is controlled by the w/s ratio. Higher w/s ratios increase sorptivity, and SF usage beyond 5 % negatively impact sorptivity. Mechanical properties are influenced by Ca/Si, Al/Na and Na/Si ratios. Grey Relational Analysis was utilized to ascertain the optimal mixture proportions, taking into account the interdependencies among multiple responses. The analysis resulted in recommending 10 % equivalent NaOH, 5 % replacement of SF, a water-to-solid (w/s) ratio of 0.50, and an excess paste content of 32 %. The study also demonstrates the rational evaluation of mix design through an illustrative example.
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•Industrial-grade powdered chemicals with lower purity are used to activate the precursors.•The aggregate system is optimized by the packing density method.•The optimal percentage of the binder is obtained by Taguchi-GRA analysis.•The optimal mix is 10 % equivalent NaOH% (level 3), 5 % of SF replacement (level 1), w/s as 0.50 (level 2) and excess paste content of 32 % (level 4).
Although including wurtzite (ZnO) in cementitious materials significantly enhances gamma-radiation mitigation, its use is not recommended as it excessively prolongs the setting time and negatively ...affects the early strength. Hence, this study attempts to address these issues while enhancing radiation-shielding by including Zn-Al-CO3 layered double hydroxide (LDH) as an alternative for ZnO. Wurtzite and LDH nanoparticles were laboratory-prepared via the co-precipitation method; their specific surface areas were found to be 2290 and 65483 cm2/g, respectively, referring to the high reactivity of LDH. Five pastes were prepared; alkali-activated slag was used as a control specimen (0 wt% nanoparticles), while the others contained 0.5 and 1 wt% ZnO or LDH. The comparative study showed that incorporating Zn-phase as LDH solved the abovementioned problems. The setting time of LDH-modified specimens fits in the standard limit (50–375 mins), while others contain ZnO exceed this limit. The inclusion of 0.5 wt%LDH showed a remarkable enhancement in mechanical performance; compressive-strength values increased by 36.2 and 31.1 % concerning the control specimen after 1 and 28-days, respectively. In contrast, the same dose of ZnO reduced strength by 26.3 and 13 %. Moreover, the LDH-modified specimens displayed the highest linear-attenuation coefficient and lowest half-value layer when exposed to two gamma-ray sources (Co-60 and Cs-137). The X-ray diffraction, thermogravimetric analysis and scanning electron microscope proved that the formation of Zn(OH)2 in the ZnO-modified specimens is the main reason behind high retardation and reduction in compressive-strength. The filling/active-seeds/chemical-reactivity actions of LDH resulted from its high surface area, forming a high amount from different strength-giving-phases (compact structure) in the LDH-modified specimens.
•The inclusion of Zn/Al-CO3 LDH to AAS fresh pastes did not exceed the standard limit of initial/final setting times.•The incorporation of 0.5 %LDH developed the compressive strength of AAS pastes.•Zinc oxide nanorod acted as a retarder during alkali-activation process.•Alkali-activated pastes modified with 0.5 %LDH paste exhibited the highest values of linear attenuation coefficients.
In this study, the size effect on the strength of wastewater concrete under freeze-thaw cycles was evaluated. Cube specimens of wastewater concrete with side lengths of 40 mm, 100 mm, 150 mm, and ...200 mm were prepared, and the resulting compressive and splitting tensile strengths after exposure to 0, 10, 20, 30, 40, and 50 freeze-thaw cycles were determined. The results show that the size effect is increasingly affected by freeze-thaw cycles with the increase in the number of cycles, while the corresponding specimen brittleness is gradually reduced, and the plasticity is enhanced. The modified Bažant size effect model considering the effect of freeze-thaw cycles on size effect was established. The modified size effect curve considering the freeze-thaw damage can be used to predict the initial strength of specimens after freeze-thaw cycles. The predicted data points were mainly distributed on the size effect curve and could directly reflect the size effect phenomenon of wastewater concrete without freeze-thaw cycles.
•A modified Bažant size effect model considering freeze-thaw damage was established.•The strength size effect regularity of wastewater concrete under freeze-thaw cycle is revealed.•Based on the modified model, the initial strength of wastewater concrete could be predicted.
•Effectiveness of calcium aluminate cement (CAC) was identified under high temperatures.•A comparative study with ordinary Portland cement (OPC)-based UHPC was performed.•An efficient CAC-based UHPC ...was developed without explosive spalling.•Thermo-mechanical properties were studied under high temperatures.•Mechanisms of spalling resistance and thermo-mechanical properties were explored.
Conventional ordinary Portland cement (OPC)-based UHPC is vulnerable to explosive spalling under high temperatures. This study aims to classify the role of calcium aluminate cement (CAC) as the substitution for OPC in UHPC under high temperatures and finally develop an efficient UHPC without explosive spalling. It was found that CAC-based UHPC (UHPC-CAC) and OPC-based UHPC (UHPC-OPC) reached their peak strength both at 250 °C, but the peak strength (153.8 MPa) of UHPC-CAC was higher than that (137.5 MPa) of UHPC-OPC. Explosive spalling was found in UHPC-OPC after reaching 500 °C, while no spalling was observed in UHPC-CAC even at 1000 °C. The effectiveness of CAC in reducing the mechanical degradation and preventing the spalling of UHPC was attributed to three potential mechanisms: (1) CAC had less physically bound water to cause the vapor pressure in UHPC; (2) The main hydration product (i.e., calcium aluminosilicate hydrates) decomposed to a lesser extent, compared to the hydration product (i.e., calcium silicate hydrates) of OPC, as proved by X-ray diffraction (XRD) analysis, Thermogravimetric analysis (TGA), and Fourier-transform infrared (FTIR) analysis; (3) there exists pores coarsening in UHPC-CAC, as evidenced by micro-XCT, which could release the water pressure in UHPC and thus prevent the spalling at elevated temperatures.
•Direct determination of UCS of rocks in different states of peninsular Malaysia.•Determination of basic rock strength parameters.•Prediction of UCS of rocks using hybrid particle swarm ...optimization-based ANN.•Prediction of UCS using conventional ANN.
Many attempts have been made to predict unconfined compressive strength (UCS) of rocks using back-propagation (BP) artificial neural network (ANN). However, BP-ANN suffers from some disadvantages such as slow rate of learning and getting trapped in local minima. Utilization of particle swarm optimization (PSO) algorithm as a mechanism to improve the performance of ANNs is recently underlined in literature. The objective of this paper is to develop a PSO-based ANN predictive model of UCS. For this reason, a comprehensive experimental program was conducted on 66 granite and limestone sample sets taken from different states in Malaysia. The experimental program consists of direct and indirect estimation of UCS of rocks. The results of laboratory tests including point load index test (IS(50)), Schmidt hammer rebound number (SRn), p-wave velocity test (Vp) and dry density (DD) test were used as inputs of the network while UCS results were set to be the output. For comparison purpose, the prediction performance of the proposed hybrid model was checked against that of a conventional ANN. Comparison between the coefficients of determination, R2, obtained through conventional ANN and PSO-based ANN techniques reveal the superiority of the PSO-based ANN model in predicting UCS. In overall, the R2 for the proposed hybrid predictive model was 0.97 while in case of conventional ANN, the R2 was found to be 0.71. By performing sensitivity analysis, it was concluded that the effect of DD and SRn on predicted UCS values is slightly higher compared to other parameters.
