The thermal conductivity (k-value) of cement-based materials like concrete is an important factor when considering the amount of heat transfer through conduction. The amount of heat loss through walls and roofs has a direct effect on the energy consumption of buildings. The steady state and transient methods are considered the two main thermal conductivity measurement approaches. The moisture content, temperature, type of aggregate, type of cementitious material and density of concrete are influential factors on the thermal conductivity. The aim of this paper is to review the techniques most commonly used to measure the thermal conductivity of concrete as well as to consider the factors affecting the thermal conductivity of cement-based materials. In addition, a general equation for predicting the thermal conductivity of concrete is proposed in this study based on data reported by researchers. The results of this review indicate that most researchers have measured the k-value of cement-based materials based on transient methods. The reported k-value in saturated conditions is higher than in dry conditions. Moreover, the measured k-value exhibits a declining trend with increasing temperature. It is concluded that using lightweight concrete in structural and non-structural building envelopes is a valuable method of reducing the amount of heat transfer and energy consumption owing to the lower k-value of lightweight concrete compared to normal weight concrete.

Thermal conductivity of concrete – A review

A novel building material with low thermal conductivity: Rapid synthesis of foam concrete reinforced silica aerogel and energy performance simulation

Fabrication of superhydrophobicity on foamed concrete surface by GO/silane coating

Experimental research on a feasible rice husk/geopolymer foam building insulation material

Thermal deformability of recycled self-compacting concrete under cyclical temperature variations

Thermal conductivity and mechanical properties of porous concrete materials

The lightweight AA2050 alloy exhibited an excellent specific strength in the T8 state. However, its widespread application was somewhat limited by the service temperature. In order to evaluate the suitability of the alloy operated at the high temperature, the high temperature mechanical properties (room temperature-300 °C) of a T8 treated AA2050 alloy were systematically investigated in this work. The results reveal that the ultimate tensile strength decreased from 566 MPa to 262 MPa as the tensile temperature increased from room temperature to 300 °C. Particularly, the rate of strength decline increased obviously at 300 °C. The elongation increased first and then decreased, reaching the maximum (12.8%) at 250 °C. The increase of tensile temperatures promoted the coarsening of T1 phases, the reduction of dislocation densities, and the decreasing fraction of deformation textures, responsible for the decrease of strengths. The high rate of strength decline at 300 °C can be attributed to the T1 phase's thickening. Meanwhile, as the tensile temperature increased from room temperature to 250 °C, the increase of the elongation resulted from more grains with lower Taylor factor and the formation of precipitation-free zones. However, the sub-grain structure caused by dynamic recovery formed and T1 phases coarsened along sub-grain boundaries, which caused the elongation decline of the alloy at 300 °C. 

Detailed investigation on high temperature mechanical properties of AA2050 Al–Cu–Li alloys

The influences of pre-rolling deformation (0–20 %) on the creep behavior, mechanical properties, corrosion behavior, and microstructures of solid solution AA2050 alloys were investigated during creep aging. The results show that the pre-rolling induced a large number of dislocations, which decreased the primary creep rate but increased the steady creep rate. As the pre-rolling strain increased from 0 % to 20 %, the peak-aged time of creep-aged alloys decreased from 40 h to 16 h, improving both yield strength (YS, from 474 MPa to 554 MPa) and ultimate tensile strength (UTS, from 522 MPa to 590 MPa). The elongation (EL) decreased from 11.2 % to 7.8 %. The strength enhancement originated from inhibited oriented precipitation effect, dislocation density increment, and dense T1 phases precipitation. Meanwhile, the area fraction of corrosion pits (fpits), intergranular corrosion (IGC) depth and stress corrosion cracking (SCC) susceptibility index (ISSRT) decreased from 7.13 %, 176 μm, and 6.1 % to 5.11 %, 33 μm, and 1.5 %, respectively. The increased resistances of pitting corrosion/IGC/SCC were attributed to the coarsening and Cu enrichment of grain boundary precipitates (GBPs), the formation of precipitation-free zones (PFZs) and low-angle grain boundaries (LAGBs), and the precipitation of T1 phases along dispersoids. 

Enhanced strength and corrosion resistance of creep-aged AA2050 Al-Li alloy by pre-rolling deformation

Quantitative effects of pre-deformation prior to non-isothermal aging on the mechanical properties-microstructure relationships in an Al-3.51Cu-1.01Li alloy

The invention provides a novel foam concrete foam stabilizer which consists of a foam stabilization copolymer formed by perfluoroalkyl ethylene acrylate, N-vinyl pyrrolidone and maleic anhydride, tertiary butanol, polysaccharide gum and water. The novel foam stabilizer is a water-soluble macromolecule formed by polymerizing free radicals, the foam viscosity is improved, the liquid surface tension is reduced, the foam stabilizer has a good effect in repairing and protecting the foam, and the problem that the compounded anionic, cationic and nonionic surfactants are low in compatibility is solved, so that the foam also has a higher stability under hard water, strong base and high-temperature conditions; and meanwhile, the foam stabilizer has the function of obviously dispersing and wetting cement slurry, and the phenomena that the foam concrete has high dry shrinkage and multiple communicating holes and the like can be effectively avoided. By employing the foam stabilizer, the compressive strength of the prepared 400-level foam concrete 28d reaches 1.8-2.3MPa under the condition of the external temperature of 40-60 DEG C, the water absorption rate is 10-15 percent, and the heat conductivity coefficient is 0.062-0.079W(m.K).

Haoran Li

Papers

Thermal conductivity and mechanical properties of porous concrete materials

Detailed investigation on high temperature mechanical properties of AA2050 Al–Cu–Li alloys

Enhanced strength and corrosion resistance of creep-aged AA2050 Al-Li alloy by pre-rolling deformation

Quantitative effects of pre-deformation prior to non-isothermal aging on the mechanical properties-microstructure relationships in an Al-3.51Cu-1.01Li alloy

Novel foam concrete foam stabilizer and preparation method thereof