Hydration Of Cement Mortars Research Articles

Mechanical properties and drying shrinkage of graphite tailing-basalt fiber cement mortar

By replacing part of standard sand with graphite tailings (GT) and adding green basalt fibers (BF) together to prepare cement mortar, it could effectively alleviate the environmental problems caused by the massive discharge of tailings and the shortage of resources caused by the massive use of natural river sand. In this study, graphite tailings and basalt fibers were added to cement mortar, and the impact of mixing GT and BF fibers on the mechanical characteristics and drying shrinkage properties of cement mortar were analysed through experimental studies. The hydration of cement mortar was investigated by using techniques such as energy spectroscopy (EDS), differential thermogravimetric analysis (DTG-TG), electron microscopy (BSEM, SEM), and x-ray diffraction (XRD). And the microstructures of the matrix, fiber, and fiber–matrix interface underwent evaluation. The findings demonstrated that the cement mortar with a 20 % GT substitution rate and 0.1 % BF by volume admixture was the most optimized combination, and the compressive strength and flexural strength at an estimated 28 days of curing time were improved the most, by 13.89 % and 14.08 %, respectively. And the early drying shrinkage performance could be improved more substantially; the drying shrinkage at the age of 7 days was 54 % that of cementitious sand. According to the microscopic test results, it was known that GT would adversely affect cement hydration due to higher sulphide levels, but it had a pozzolanic effect. The appropriate amount of GT could give full play to the pozzolanic effect, reduce the porosity of cement mortar and lower the Ca/Si value within the matrix–matrix fiber interface transitional region, improve the adverse effect of its sulphide on cement mortar, and help improve the mechanical and crack-resisting properties of cement mortar.

Effect of aggregate size on water distribution and pore fractal characteristics during hydration of cement mortar based on low-field NMR technology

The influence of aggregate size (AS) on the hydration of cement mortar is very important for improving the quality and stability of cement mortar. This study aims to study the effect of AS on water distribution and pore structure characteristics on the early-age hydration of cement mortar by low-field NMR technology. The hydration degree and fractal dimension of the hydration process were calculated by the T2 spectrum. The water distribution models at different times and locations during the hydration process were established based on the MRI bitmap data. The variation law of water volume at different locations was studied. The results indicate that: In the process of hydration, some of the water is consumed by the hydration reaction, and some of the water oozes out. The water in the large pores flows to the small pores under the action of hydrostatic pressure. AS affected the uniformity of the cement mortar at the initial state, and the gradation of the sand could improve the uniformity. The smaller AS was, the more complex the pore water distribution and changed during hydration. The bleeding mass was directly proportional to the porosity and inversely proportional to the specific surface area of particles. The effect of porosity on bleeding mass was more significant than AS. Pore fractal dimension was negatively correlated with aggregate diameter. In the initial stage, when the aggregate composition became complex, the change of fractal dimension with time also became complex. The fractal dimension increased gradually with the increase of hydration time. The gel pores (G) did not have fractal characteristics from beginning to end, capillary pores (C) and transition pores (T) had fractal characteristics after a particular time of hydration reaction. Although the air-voids (A) had fractal characteristics from beginning to end, they were not continuous.

Effect of lime mud under wet grinding on the compressive strength and hydration of cement mortar

Lime mud, an alkaline solid waste used to cause environmental problems now is a potential mineral additive in building material. In this paper, sodium hexametaphosphate (SH) and sodium stearate (SDS) were used to pretreat lime mud during wet grinding to make two modified lime muds, respectively. Incorporation of the 10% lime mud (not pretreated or pretreated by wet grinding without modifiers) reduced the fluidity of cement mortar, but the mortar containing 10% modified lime mud show a similar fluidity with the reference. The effect of modified lime mud on the compressive strength and hydration of cement mortar was evaluated by X-Ray Diffraction (XRD), Fourier transform infrared spectrometer (FTIR), Thermogravimeter (TG-DTG) and Scanning electron micrograph-energy dispersive spectrometry (SEM-EDS). The results showed that the lime mud pretreated by wet grinding with 1% SH had the great bonding property with hydration products, and the optimal replacement ratio was 10% in cement mortar.

Long-term performance and hydration of cement mortars with hydroxyethyl methyl cellulose cured at 5℃ low temperature

As one of the special curing regimes, low temperature environment is considered to be crucial to the development of various properties of cementitious materials. This work focuses on the long-term performance and hydration of cement mortars with hydroxyethyl methyl cellulose (HEMC) cured at 5℃. The results show that the mid-late flexural and compressive strengths decrease with the HEMC content increasing, to get the lowest values at 1% HEMC. Afterwards, with the HEMC content increasing to 3%, the above strengths gradually increase, still being lower than those of the control. The tensile bond strength increases with the HEMC content increasing, to reach the maximum value at 0.3–0.5% HEMC, and then decreases with the HEMC content increasing to 3%, which is still much higher than that of the control. The drying shrinkage presents a significant increase with the HEMC content increasing. Moreover, HEMC significantly retards the early hydration of cement pastes. But the final hydration degree of cement pastes with HEMC tends to be close to that of the control. In addition, macro pores and the total porosity increase with the HEMC content increasing at 0–1%, and then decrease to some extent at 3% HEMC. Obviously, due to its better long-term properties at 5℃, the cement mortars with HEMC are still applicable at low temperatures.

Dispersion and effects of metal impregnated granular activated carbon particles on the hydration of antimicrobial mortars

Granular activated carbon (GAC) particles impregnated with antimicrobial metals were incorporated into cementitious materials for the express purpose of inhibiting biogenic concrete corrosion. We report herein the influence of such metal-laden GAC particles on the hydration of cement mortars when substituted for fine aggregate, as well as the dispersion of metal in the cured matrix. Isothermal calorimetry was utilized to study the influence of GAC without and with copper and/or cobalt on select hydration characteristics of ordinary portland cement (OPC) mortars. When 1% of the fine aggregate mass was replaced with GAC particles of similar size, total evolved heat in all formulations was similar, regardless of GAC pretreatment. However, as the substitution approached 10% of the fine aggregate mass, metal-laden GAC formulations imparted delays in heat liberation and lowered heat fluxes. Results also substantiate that metal-laden GAC particles participate in the enhanced uptake of the calcium that is normally liberated during cement mixing and that the water delivered with GAC particles is not readily available during the first 142 h of curing. Electron microprobe analysis (EMPA) elucidated that copper and cobalt were homogenously distributed throughout the cement paste with metal-laden GAC, with these metals concentrations localized in a 50–100 μm region surrounding the GAC particles. Compressive strengths were not affected by the presence of metal-impregnated GAC in the concentration ranges tested and reported herein.

The Influence of Limestone Powder on Fluidity, Strength and Hydration of Cement Mortar

An experimental program has been conducted to investigate the influence of limestone powder (LP) on fluidity, strength, and hydration of cement mortar. Four laboratory grinds were prepared using a ball mill. The relationship between roundness of the LP and water requirement of paste, fluidity and strength of mortar was studied. The influence of LP on hydration of cement was investigated. Hydration products were determined by X-ray diffraction (XRD) analysis. Test results show that the roundness of LP significantly affected the water requirement of paste, fluidity and strength of mortar. In addition, the sites for the nucleation and growth of hydration products, provided by LP, accelerate the hydration of cement at early ages. While the enhancement of cement hydration at later ages mainly due to the formation of calcium aluminate monocarbonate.