Correlative Mechanism of Hydraulic-mechanical Property in Cemented Paste Backfill

Hydraulic characteristic is a good indication of binder hydration, which determines the strength development of cemented paste backfill（CPB）. Therefore, the hydraulic characteristic should be communicated with the mechanical property to provide an advanced knowledge that can help mine workers make a rational strategy and reduce the mining cycle. An experimental program was performed to obtain the hydraulic（monitored by suction and volumetric water content） and mechanical properties（unconfined compressive strength（UCS） test） of CPB at the 28 days curing age. According to the monitoring and testing results, the relationships between the hydration reaction rate and volumetric water content（VWC）, suction and VWC, suction and UCS were established. The hydration degree showed a liner rise as the VWC decreased. Curves of the VWC and UCS were featured with a nonlinear reduction and nonlinear growth（both are exponential functions） as the suction rising, respectively. These established relationships validated the strong correlative mechanism of hydraulic and mechanics behavior for CPB. Also, the results of the present research indicated that the hydraulic characteristics and mechanical property were strongly coupled. These correlations and couplings will be of great importance to understand the hardening process of CPB and bring to a safe CPB field operation.

Innovative Production of PCMs （Phase Change Materials） Preparation by Vacuum Impregnation： Mechanical Strength of Mortars Cement with Composite PCMs Content

An experimental investigation was conducted to study the efficiency of thermal insulation of composite PCMs （phase change materials） produced by vacuum impregnation process between paraffin （PCMs） and fly ash particles. DSC （differential scanning calorimeter） has been used to determine the thermal properties of latent heat of melting and heat capacity for composite PCMs. Vacuum impregnation pressure of 40 in.Hg, paraffin melting temperature of 90℃, vacuum time and impregnation time of paraffin of 30 min are the optimum condition of composite PCMs productions. The values of latent heat of melting and heat capacity are 74.00 J/g and 15.726 J/g.℃ for composite PCMs that produces by the optimum condition in vacuum impregnation process. Increasing the amount of composite PCMs replacing for cement in mortars causes the compressive strength, flexural strength and tensile strength reduction. Compressive strength, flexural strength and tensile strength of mortar with and without composite PCMs can be increased by the longer time of water curing for mortar specimens. Thermal conductivity （k） of mortar cement is reduced by increasing the amount of composite PCMs which replaced for cement in mortar plate compositions. Composite PCMs have the efficiency for thermal energy insulation when incorporated into the buildings. Therefore, this property of paraffin/fly ash composites PCMs can reduce the energy consumption for temperature control in the buildings.

Experimental Investigation of the Impact of Compression on the Petro-Physical and Micromechanical Properties of Wellbore Cement Containing Salt

In this study, we investigated the effect of compression on the micromechanical and the petro- physical properties of salted wellbore cement systems. The experiments were conducted using a customized bench scale model, which utilized an expandable tubulars simulating the compression of a previously cemented casing under field-like conditions. The “mini-wellbore model” sample consisted of a pipe inside pipe assembly with a cemented annulus. The cement samples were cured in a water bath for 28 days prior to the compression experiments to allow adequate hydration. The impact of compression on the cement’s petro-physical and mechanical properties was quantified by measuring the porosity, permeability and hardness of salt cement cores drilled parallel to the orientation of the pipe from the compacted cement sheath. Permeability (Core-flood) experiments were conducted at 21℃, 10,342 kPa confining pressure for a period of 120 minutes. During the core-flood experiments, conducted using Pulse-decay method, deionized water was flowed through cement cores to determine the permeability of the cores. The results obtained from these experiments confirmed that the compression of the cement positively impacted the cements ability to provide long term zonal isolation, shown by the effective reduction in porosity and permeability. Furthermore, the results confirm reduction in the detrimental effect of salt on the strength and stiffness in post-compression cement.

Evaluation of the effect of sodium silicate addition to mine backfill,Gelfill-Part 2:Effects of mixing time and curing temperature

The effects of mixing time and curing temperature on the uniaxial compressive strength （UCS） andmicrostructure of cemented hydraulic fill （CHF） and sodium silicate-fortified backfill （Gelfill） wereinvestigated in the laboratory. A series of CHF and Gelfill samples was mixed for time periods rangingfrom 5 min to 60 min and cured at temperatures ranging from 5 C to 50 C for 7 d, 14 d or 28 d.Increasing the mixing time negatively influenced the UCS of Gelfill samples, but did not have a detectableeffect on CHF samples. The curing temperature had a strong positive impact on the UCSs of both Gelfilland CHF. An elevated temperature caused rapid UCS development over the first 14 d of curing. Mercuryintrusion porosimetry （MIP） indicated that the pore size distribution and total porosity of Gelfill werealtered by curing temperature.

Evaluation of the effect of sodium silicate addition to mine backfill,GelfillLPart 1

In this paper, the mechanical properties of sodium silicate-fortified backfill, called Gelfill, were investigated by conducting a series of laboratory experiments. Two configurations were tested, i.e. Gelfill and cemented hydraulic fill（CHF）. The Gelfill has an alkali activator such as sodium silicate in its materials in addition to primary materials of mine backfill which are tailings, water and binders. Large numbers of samples of Gelfill and CHF with various mixture designs were cast and cured for over 28 d. The mechanical properties of samples were investigated using uniaxial compression test, and the results were compared with those of reference samples made without sodium silicate. The test results indicated that the addition of an appropriate amount of an alkali activator such as sodium silicate can enhance the mechanical（uniaxial compressive strength） and physical（water retention） properties of backfill. The microstructure analysis conducted by mercury intrusion porosimetry（MIP） revealed that the addition of sodium silicate can modify the pore size distribution and total porosity of Gelfill, which can contribute to the better mechanical properties of Gelfill. It was also shown that the time and rate of drainage in the Gelfill specimens are less than those in CHF specimens made without sodium silicate. Finally, the study showed that the addition of sodium silicate can reduce the required setting time of mine backfill, which can contribute to increase mine production in accordance with the mine safety.