Selective Tests of Grouting Material for Fractured Coal and Rock Masses in a Water-borne HS Environment
Coal mining is vulnerable to multiple kinds of threat from water incursion. Many coal seams contain dissolved H2S, which may be released during mining, seriously endangering the health of workers. Orthogonal testing was used to analyze the physical and mechanical properties of composite slurries in different proportions. The results showed slurry with a water-solid ratio of 0.8:1 to have the optimal combination of properties. A uniform experimental method was used to investigate the impact of the water-cement ratio, concentration of sodium silicate, and volume of cement-sodium silicate (CS) on the setting time and consolidating strength of CS slurry. This paper provides the appropriate application scope of two grouting materials (optimized composite slurry and CS slurry), based on experimental data and the results of a large number of in situ trials. Finally, the optimized composite slurry and cement-sodium silicate slurry were used to carry out grouting of the center auxiliary transport roadway of the 3 coal seam at the Ningtiaota Coal Mine, operated by the Shaanxi Coal Industry Group. It was shown that the type and formula of the slurry could be changed in a timely manner, based on the water outlet and concentration of H2S at the site, achieving successful grouting reinforcement and seepage-proofing.
Experimental characterization and performance evaluation of geothermal grouting materials subjected to heating–cooling cycles
Abstract In recent years, the increasing rise in environmental awareness among energy consumers has led to an increasing use of renewable energies such as the geothermal energy. An important role in the efficient exploitation of the geothermal resource is played by the grouting material placed in the borehole between the pipes and the ground. Actually, the use of proper grouts is essential to provide an effective heat transfer between the ground and the heat carrier fluid in the pipes, and also to comply with the mechanical and environmental demands. However, when it comes to the construction of the GHP installations, the grout is especially required to be easy to work with (workable) and for this reason more water than required is sometimes added. In order to assess the suitability of grouting materials with significant water/solid ratios, the thermal conductivity, mechanical strength and permeability of five different grouts and grout–pipe specimens were measured for their laboratory characterization. In addition, the grouts were subjected to heating and cooling cycles to evaluate their durability with time in terms of the potential degradation of the materials and the loss of quality of the grout–pipe interface. According to the results obtained, the grouts here tested are appropriate for most of the geothermal heat pump installations, especially for those with low to medium ground thermal properties.
Influence of supplementary cementitious materials on engineering properties of high strength concrete
Abstract The influence of supplementary cementitious materials (SCMs), namely silica fume, metakaolin, fly ash and ground granulated blast-furnace slag, on the engineering properties of high strength concrete (HSC) has been investigated in this study. Workability, compressive strength, elastic modulus, porosity and pore size distribution were assessed in order to quantify the effects of the different materials. The results show that the inclusion of the different SCMs has considerable influence on the workability of HSC. Silica fume and metakaolin significantly enhanced the strength of HSC. Fly ash reduced the early-age strength; however, it enhanced the long-term strength of the HSC. Likewise, ground granulated blast-furnace slag impaired the early-age strength, but marginally improved the long-term strength at low replacement levels. The general effect of the different SCMs on the elastic modulus of HSC is rather small compared to their effect on strength. There are good correlations between both static and dynamic moduli and compressive strength. The EC 2 and ACI 209 provide a good estimate of static modulus of elasticity from compressive strength, while the BS8110 gives a good estimate of static modulus of elasticity from dynamic modulus of HSC containing the different SCMs. Porosity and pore size were reduced with the addition of the different SCMs. The volume of mesopores in the ranges of