Durability of sea-sand containing concrete:Effects of chloride ion penetration

This paper describes an orthogonal experiment on the effect of water/cement ratio,water consumption per cubic meter,curing time,and type of sand on the response＂resistance to chloride ion penetration＂.A sea-sand containing concrete was used for the trials.An analysis of chloride ion diffusion coefficients at different factor levels was performed.A predictive model of chloride ion diffusion in concrete is developed through regression analysis.The experimental results show that when the water/cement ratio varies from 0.45 to 0.60,and the water consumption per cubic meter varies from 185 to 215 kg,and the curing time varies from 30 to 180 d then the size of the effects fall in the order（most significant first）： curing time,type of sand,water consumption per cubic meter,and water/cement ratio.Chloride ion penetration is reduced,and better durability of the concrete is observed,with longer curing times,less water consumption per cubic meter,and a smaller water/cement ratio.

Effects of strain rates on mechanical properties of limestone under high temperature

The experimental tests for limestone specimens at 700 °C in uniaxial compression were carried out to inves- tigate the mechanical effects of loading rates on limestone by using a MTS810 rock mechanics servo- controlled testing system considering the loading rate as a variable. The mechanical properties of limestone such as the stress-strain curve, variable characteristics of peak strength and the modulus of elasticity of limestone were studied under the strain rates ranging from 1.1 10à5 to 1.1 10à1 sà1. (1) Sharp decreases were shown for the peak strength and elastic modulus of limestone from 1.1 10à5 to 1.1 10à4 sà1 at 700 °C as well as a downward trend was shown from 1.1 10à4 to 1.1 10à1 sà1 with the rise of the strain rate. (2) The peak strain increased from 1.1 10à5 to 1.1 10à4 sà1, however, there was no obvious changes shown for the peak strain of limestone from 1.1 10à4 to 1.1 10à1 sà1. These results can provide valuable references for the rock blasting effect and design of mine.

Macroscopic and microscopic fracture features of concrete used in coal mine under chlorine salt erosion

The microscopic morphology and pore structure characteristics of concrete with composite admixtures(fly ash and mineral powder) after chlorine salt erosion were analyzed via scanning electron microscopy(SEM) and mercury injection porosimetry(MIP), providing the basis for the design and maintenance of concrete shafts in coal mines. The above-mentioned characteristics were compared with the macroscopic characteristic of concrete fractures under uniaxial compression. The results show that the macroscopic fracture characteristics of concrete under uniaxial compression change from longitudinal split fracture and oblique section shear fracture to conjugate cant fracture, and the degree of breakage increases.Interface cracks, cement paste cracks, spherical surface cracks, and aggregate cracks appear in concrete under uniaxial compression. In the early stages of corrosion, the original cracks which are obvious are repaired. When the corrosion becomes more serious, cement paste cracks appear, and the number of harmful holes increases while the number of harmless holes decreases. This study also reveals the relationship between the macroscopic properties and microscopic structure of concrete under chloride salt erosion. Finally, the paper preliminarily discussed the relationship between the macroscopic properties and mesoscopic characteristics of concrete under chlorine salt erosion.

Meso-structure and fracture mechanism of mudstone at high temperature

The meso-structure mineral composition and fracture mechanism of uniaxial compressed mudstone samples at high temperature were analyzed by XRD and scanning electron microscopy. The effect of tem- perature on mudstone composition and fracture mechanism were studied from a meso-structural per- spective, and the relationship between meso-structure and macro-mechanical characteristics at high temperature was revealed. The findings demonstrated that the fluctuation in diffraction intensity of kao- linite in the mudstone caused the fluctuation in its mechanical properties. The overall structure under- went a phase change around 600℃, which led to the sudden change in the mechanical properties of mudstone samples. When the temperature reached 600 ℃, the crystalline state worsened and kaolinite disappeared; however, some illite was produced, indicating that the chemical reaction of the structure and sudden drop of bearing capacity of the mudstone. Mudst0ne fracturing at high temperature involves mainly intergranular and transgranular fractures, which are typical in micro-brittle tensile failure. Con- sidering the macro-fracture characteristics of mudstone, the results suggested that macro-fracture under external force corresoonds to the meso-fracture.