Preparation and characterization of mortar mixes containing organic acid/expanded vermiculite composite PCM

In this paper, capric acid (CA) and palmitic acid (PA) binary PCM/expanded vermiculite (CA-PA/EVM) form stable composite PCM (FS-CPCM) was firstly synthesized by adsorption method. The EVM had the optimal adsorption rate when the mass ratio of CA-PA to EVM was 45:55. The FT-IR results indicated that there was no chemical reaction between binary PCM and EVM. After the thermal cycles for 50 times, the mass loss of the prepared CA-PA/EVM FS-CPCM was 2.8%. However, the latent heat was reduced by 16.10%. Furthermore, thermal energy storage (TES) mortar mixes were prepared by replacing sand aggregates with the fabricated CA-PA/EVM FS-CPCM. The effect of replacing sand aggregates with CA-PA/EVM FS-CPCM on compressive and flexural strength of the mortar mixes was investigated by mechanical experiments. The prepared mortar mixes with CA-PA/EVM FS-CPCMs aggregate exhibited good thermal performance and could be preferentially potential PCM for thermal regulation and energy saving in buildings

Preparation and Properties of Porous Concrete Based on Geopolymer of Red Mud and Yellow River Sediment

Red mud (RM) and Yellow River sediment (YRS) are challenging to handle as waste materials. In this study, RM with geopolymer and heavy metal adsorption characteristics was combined with YRS and ground granulated blast furnace slag (GGBS) to develop a porous geopolymer with high strength and high adsorption performance. A geopolymer cementitious material with high strength was prepared using high temperature water bath curing of 90 °C and different dosages of YRS, and a porous geopolymer concrete was further prepared. The compressive strength, fluidity and setting time of geopolymer cementitious materials were tested, and the compressive strength, porosity and permeability of porous geopolymer concrete were also tested. The environmental impact assessment of geopolymer cementitious materials was further conducted. The hydration products and microstructure of geopolymer gel materials were analyzed by XRD, SEM and FT-IR tests. The results show that the addition of YRS can effectively prolong the setting time of the geopolymer cementitious material, and the enhancement rate is as high as 150% compared with the geopolymer cementitious materials without the addition of YRS. An appropriate amount of YRS can improve the compressive strength of the geopolymer cementitious materials, and its early compressive strength can be further improved under the high temperature water bath curing of 90 °C, and the compressive strength at an age of 3 d can be up to 86.7 MPa. Meanwhile, the compressive strength of porous geopolymer concrete at an age of 28 d is up to 28.1 MPa. YRS can participate in geopolymer reactions, and high temperature water bath curing can promote the reaction degree. Curing method and YRS dosages have little effect on the porosity and permeability of the porous geopolymer concrete. The porous geopolymer has a good heavy metal adsorption effect, and the alkaline pH values can be gradually diluted to neutral

Effect of Layered Double Hydroxides on the Deterioration Process of Cement Paste under Sulfate Attack

This study investigated the effect of layered double hydroxides (LDHs) on the deterioration process of cement paste in the sulfate environment. Cement pastes with the addition of original and calcined LDHs at 2.5 wt.% and 5.0 wt.% of cement were exposed to Na2SO4 solution for 360 days. The macroscopic performance of the cement paste was assessed based on mass variation, porosity, compressive strength, and content of sulfate ions. Furthermore, the microhardness, microstructures, and composition of the degraded pastes were examined using Vickers hardness (HV), mercury intrusion porosimetry (MIP), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The results indicate that cement paste incorporated with LDHs can mitigate the corrosion caused by sulfate effectively, especially in the case of calcined LDHs (C-LDHs), which primarily increase the adsorption of sulfate. Compared with the control specimen, the 180 d compressive strength loss ratio of specimens with 2.5 wt.% and 5.0 wt.% of C-LDHs decreased by 63.66% and 80.51%, respectively. Moreover, LDHs can reduce the amount of ettringite crystals, densify the microstructure, and refine the pore structure to mitigate the cement paste’s sulfate corrosion significantly. Compared with the control specimen, the 180 d harmful pore volume fraction of specimens laced with 2.5 wt.% and 5.0 wt.% C-LDHs decreased by 43.77% and 54.51%, respectively. In terms of the content of C-LDHs, an optimal content of C-LDHs could ensure the dominant effect of adsorption, while excessive C-LDHs could refine pores. In addition, Vickers hardness has an excellent correlation with compressive strength, which could precisely predict the compressive strength. Moreover, by combining the Vickers hardness distribution and content distribution of sulfate ions, the cross-section of the paste could be classified into four regions to evaluate the deterioration process accurately: the degraded zone, the strengthened zone, the invaded zone, and the intact zone

Influence of curing temperature on freeze-thaw resistance of limestone powder hydraulic concrete

Limestone powder (LS) is a new environmentally-friendly concrete admixture, and its application in concrete engineering is worth exploring. The curing of LS hydraulic concrete under extreme temperatures will significantly affect the interior microstructure of concrete, which has a significant impact on the resistance to freeze-thaw cycles. This study aims to investigate the influence of LS replacement quantity (10 %, 30 % and 50 %) and curing temperatures (5 ℃, 20 ℃ and 50 ℃) on the freeze-thaw resistance of hydraulic concrete. The freeze-thaw resistance was reflected by the mass loss rate, relative dynamic modulus of elasticity (RDM) and ultrasonic inspection. The hydration products, microstructure and pore composition of LS hydraulic concrete were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) to dissect the underlying mechanisms behind the freeze-thaw resistance. The relationship between the pore composition and the mass loss rate and RDM was established to connect the microcosmic properties with the macroscopic properties. Findings from this study provide a guidance for the application of LS in concrete engineering under harsh environments

Properties of cement mortar containing recycled glass and rice husk ash

Using recycled glass (RG) to replace river sand in the production of cement-based materials saves the increasingly depleting natural sand resources. Previous studies have shown that the smooth surface and reactive silica of RG adversely affected its bonding with the cement paste and thereby caused a potential alkali-silica-reaction (ASR). This study used rice husk ash (RHA) as an eco-friendly mineral admixture to ameliorate the properties of the RG incorporated mortar. A fixed replacement of 50% RG was used to replace sand, while varying proportions (10%, 20% and 30%) of RHA were adopted to replace cement. For comparison, a mixture containing only sand and cement was used as the reference sample. The flexural and compressive strength, water absorption, ASR expansion, and rapid chloride mitigation (RCM) of the hardened samples were evaluated. In addition, SEM, XRD, and TG analysis were employed to analyze the microstructures and chemical compositions of different samples. The results showed that incorporating RG as a river sand replacement in cement mortar reduced flexural and compressive strength and increased water absorption and chloride ion penetration. Moreover, the ASR expansion value (0.34%) was beyond the permissible limit (0.1) indicated by the ASTM C1260. The addition of RHA improved the mechanical properties and durability of the cement mortar at a later curing age as a result of the RHA-induced pozzolanic reaction and micro-filler effect. By converting portlandite (CH) derived from cement hydration into secondary C-S-H, the use of RHA greatly reduced the porosity (augmenting the compressive and flexural strength) and concurrently suppressed the RG-induced ASR expansion. The results of XRD, SEM and TG analysis corresponded well with the macro-property analysis and helped to elucidate the underlying mechanisms of the RHA-induced beneficial effects. Findings from this study provide new insights into the potential use of eco-friendly RHA in addressing the mechanical and durability problems associated with the use of RG as aggregate in cementitious materials. (c) 2021 Elsevier Ltd. All rights reserved