Search

Carbon capture utilization and storage technique (CCUS) is an effective way to mitigate climate change. Carbon dioxide (CO2) sequestration binders (CSB) composed of hydrated lime (CH) and cement has great application prospects in CCUS. Although CH in CSB can improve the carbon absorption capacity, it causes a significant decrease in flexural strength. This study focused on the effect of polyvinyl alcohol (PVA) on the CO2 absorption capacity and flexural strength of CSB. The results show that PVA is beneficial to enhancing the flexural strength of CSB either under natural carbonation or accelerated carbonation. This enhancement is more pronounced at an early age for CSB with high CH content. Furthermore, CO2 uptake experiments show that the PVA would not reduce the CO2 absorption of CSB and even has a slight improvement effect. Finally, thermodynamic modeling and price calculation were adopted for CSB to illustrate the chemical phase and economic cost changes. The outcomes of this study shed new light on PVA to optimize CSB. [ABSTRACT FROM AUTHOR]

Limestone powder has been widely used in concrete structures because of its easy availability and positive effect on reducing the heat of hydration. The addition of limestone powder has a significant influence on the hydration and microstructure of cement paste and therefore affects the strength and durability of concrete. This paper examines the hydration and microstructure of cement paste blended with limestone powder using multiple techniques. The results reveal that when the content of limestone powder is up to 50 wt%, the compressive strength, cumulative heat and portlandite show a significant reduction. However, the addition of limestone powder has no effect on the species of hydration products and pore solution composition in cement paste specimens. The porosity and relative threshold diameter of cement paste samples increase while the pore volume (<50 nm) decreases with the increase in limestone powder content. The total electrical resistance of continuously and discontinuously connected pores in cement paste samples has an exponential relationship with the threshold diameter and a linear relationship with the pore volume (<50 nm) and porosity. [ABSTRACT FROM AUTHOR]

A commercial interest in the improvement of durability is driving efforts to develop new generation of surface-treatment agents. In the previous paper, a series of nanoSiO 2 -polycarboxylate superplasticizer core-shell nanoparticles (NS@PCE) were synthesized by “grafting to” method. In this paper, we aim to explore the potential of NS@PCE to densify the surface of cementitious materials, and to study the mechanism of nanoparticles surface-treatment process by measuring water absorption ratio, dispersion stability, pozzolanic reactivity, and mercury intrusion porosimetry. Results show that NS@PCE is effective in reducing the water absorption. Various NS@PCE present different influences, it seems that NS@PCE with a moderate shell-core ratio is a more reasonable choice. A hypothesis was proposed to explain the surface-treatment effect of nanoparticles, it utilizes two properties (dispersity and pozzolanic reactivity) of nanoparticles to describe their refining-pore performance. This research indicates a new pathway for nanoSiO 2 to optimizing cementitious materials. [ABSTRACT FROM AUTHOR]

It is generally accepted that fine particles could accelerate cement hydration process, or, more specifically, this accelerating effect can be attributed to additional surface area introduced by fine particles. In addition to this view, the surface state of fine particles is also an important factor, especially for nanoparticles. In the previous study, a series of nano-SiO2-polycarboxylate superplasticizer core-shell nanoparticles (NS@PCE) were synthesized, which have a similar particle size distribution but different surface properties. In this study, the impact of NS@PCE on cement hydration was investigated by heat flow calorimetry, mechanical property measurement, XRD, and SEM. Results show that, among a series of NS@PCE, NS@PCE-2 with a moderate shell-core ratio appeared to be more effective in accelerating cement hydration. As dosage increases, the efficiency of NS@PCE-2 would reach a plateau which is quantified by various characteristic values. Compressive strength results indicate that strength has a linear correlation with cumulative heat release. A hypothesis was proposed to explain the modification effect of NS@PCE, which highlights a balance between initial dispersion and pozzolanic reactivity. This paper provides a new understanding for the surface modification of supplementary cementitious materials and their application and also sheds a new light on nano-SiO2 for optimizing cement-based materials. [ABSTRACT FROM AUTHOR]

In this study, shrinkage reducing admixture (SRA) was grafted on NanoSiO 2 (NS) surfaces to synthesize novel core-shell (NS@SRA) particles and improve dispersion of NS in cement paste. The synthesized NS@SRA was characterized by Fourier transform infrared spectroscopy, dynamic light scattering, and thermogravimetric analysis. A series of tests were performed to investigate the effects of NS@SRA addition on the compressive strength and shrinkage of cement paste. It is found that NS@SRA increases the strength of cement paste, especially at later ages. Unlike conventional NS, which significantly increases autogenous shrinkage of cement paste, addition of NS@SRA does not appreciably affect autogenous shrinkage of the paste at early ages. Based on dispersion and zeta potential measurements of NS and NS@SRA particles in synthetic pore solution, we propose that hydration products around NS@SRA may result in gradual separation of SRA from the core. The released SRA may reduce shrinkage and mitigate cracking of cement composites at later ages. [ABSTRACT FROM AUTHOR]

• A kind of NS@GO core-shell nanoparticles was synthesized and firstly applied to reinforce cementitious materials. • The incorporation of NS@GO could more effectively enhance the mechanical property of cement composites. • A hypothesis named sandwich effect was proposed to explain the reinforcing results of NS@GO. Graphene oxide (GO) has enormous potential to improve properties of cementitious materials. Well dispersed GO in hardened cement matrix could be more effective in strengthening concrete compared to aggregated GO. While GO agglomeration is somewhat inevitable due to its fine nature, the degree of agglomeration could be tuned through particle separation. In this study, nanoSiO 2 @graphene-oxide (NS@GO) nanoparticles were synthesized using GO and colloid nanoSiO 2 (NS) by a electrostatic self-assembly method. NS, GO and the prepared NS@GO were characterized by x-ray diffraction, scanning electron microscopy, atomic force microscopy, and Fourier transmission infrared, and, the influence of NS@GO addition on the mechanical properties of cementitious composites was investigated. The results show that NS@GO can increase the flexural strength of cement composites by 49.2% at later age. A "sandwich effect" was proposed as an important reinforcing mechanism of NS@GO based on the microstructure and hydration products of NS@GO added composites. Compared with the simple NS-GO blend, NS@GO can better maintain the spatial structure of GO when mixed with cement. In addition, there would be more interactions between calcium silicate hydrates and GO during the cement hydration process, which contributes to the strength gain in NS@GO added mix. The research sheds new light on using GO and NS to optimize cementitious material design, as well as spatial coordination of different types of nanoparticles. [ABSTRACT FROM AUTHOR]

[Display omitted] • SCMs pastes by CO 2 and coupled CO 2 -standard curing were exposed to high temperature. • Coupled CO 2 -standard curing yielded the highest compressive strength at 600 ℃. • Coupled CO 2 -standard curing of SCMs pastes induced a denser pore structure at 600 ℃. • Glass powder barely showed pozzolanic reaction or carbonation promotion but was inert in cement blocks. This study seeks to understand the influence of CO 2 curing on the high-temperature performance of cement paste incorporated with different types of common supplementary cementitious materials (SCMs). The results showed that due to the simultaneous generation of CaCO 3 and hydration products, the samples carbonated for 2 days and then standard cured for 26 days (CS curing) had the best high-temperature resistance, which was reflected by higher compressive strength, lower water absorption and decreased water sorptivity. Interestingly, the porosity of the CS cured ground granulated blast furnace slag (GGBS)-incorporated cement block decreased by 26.80% after exposure to 600 ℃ due to the transformation of large loose pores into more compact small pores. Glass powder (GP) was inert in the paste matrix with no obvious pozzolanic reaction and negligible improvement of carbonation degree, leading to the lowest elevated-temperature performance; whereas, GGBS and fly ash (FA) increased the generation of CaCO 3 by 19.05% and 15.08%, respectively. Overall, findings from the present study demonstrate that the employment of CS curing of SCMs blended cement blocks has great potential to reduce carbon footprint and improve performance under elevated temperatures. [ABSTRACT FROM AUTHOR]

Highlights • DIP was applied to analysis the microstructure. • The relationship between pore size and pore shape was established. • The forming mechanisms of capillary pores was studied. Abstract Pore structure is a significant microstructural characteristic in cement-based materials and dominates the mechanical and transport properties of the materials. In this study, sectional plane analysis based on backscattered electron scanning electron microscope (SEM-BSE) images was used to provide insights into the nature of the pore structure. The effects of the w/c ratio on the total porosity and heterogeneity of the local porosity were analyzed. By coupling using Digital Image Processing (DIP) method, each single pore displayed on SEM-BSE images was captured, and the equivalent circular diameter, hydraulic radius, and roundness of each single pore were calculated to describe its size and shape characteristics. The relationship between the pore size and pore shape was also established by comparing the pore size distribution and the shape parameter distributions. Results indicates that pores become less spherical with increasing pore sizes. Status oriented model was further introduced to simulate the hydration process and investigate the forming mechanisms of capillary pores. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combined use of waste glass and RHA greatly alleviates wastes disposal at landfills. • Use of RHA improved mechanical and durability of cement mortar. • Addition of RHA suppressed RG-induced ASR expansion. • RHA holds great promise as eco-friendly pozzolanic materials. 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. [ABSTRACT FROM AUTHOR]

A microstructure-guided diffusivity model of cement paste is devised to explore the dependence of the relative diffusivity on the microstructure evolutions of cement paste from fresh state via non-spherical cement particles hydration to hardened state. The microstructure-guided diffusivity model contains three main components: (1) the microstructure of fresh cement paste is generated to simulate the initial state of non-spherical cement particles in water; (2) a continuum-based hydration model of non-spherical cement particles (HYD-NSP) is proposed to describe the evolutions of various phases (hydration products and pores) from fresh state to hardened state; (3) a random walk model is implemented to the microstructures of hydrated cement paste digitalized at the resolution of 0.1 μm/voxel for the determination of relative diffusivity of cement paste. Although this study takes five kinds of Platonic particles and sphere as an introductory example, this microstructure-guided model is readily applicable to other complex microstructures induced by the hydration of non-spherical cement particles. Finally, we utilize the framework to evaluate the influence of the geometrical shape of cement particles on the hydrated microstructure and relative diffusivity of cement paste. Results shed light on that the relative diffusivity increases with the increase of sphericity as a shape descriptor of cement particle. This is due to the specific surface area decreasing with the increase of sphericity, resulting in less hydration products and more porosity, which ultimately increases the relative diffusivity. • Microstructure of fresh cement paste with non-spherical particles is generated. • A continuous-based hydration model of non-spherical cement particles is proposed. • Evolutions of hydration products and pores in hydrated cement paste are described. • A microstructure-guided diffusivity model of cement paste is devised. • Effect of cement shape on the hydrated microstructure and diffusivity is studied. [ABSTRACT FROM AUTHOR]