Thermal conductivity of cement paste containing waste glass powder, metakaolin and limestone filler as supplementary cementitious material

Linde and Shell team up to commercialise lower-carbon technology for ethylene

Investigation of thermal conductivity and related parameters of early-age cement paste

Abstract: Carbon nanotubes (CNTs) are potential candidates to enhance the heat balance of concrete, reducing internal stresses caused by differential heating in massive concrete elements. The higher the aspect ratio (AR) and content of CNTs, the greater the expected thermal conductivity (TC). However, high AR may impair the proper dispersion of CNTs in cementitious matrix, potentially harming the workability and mechanical strength of the composite. This work evaluated the effect of the AR (35, 250, 900, and 3500) and content (0.05% and 0.10%) of CNTs on the TC, rheology (squeeze flow), and mechanical strength of cement paste. Results showed that 0.05% CNT increased the TC of paste by up to 15% for AR of 250, but further increasing AR progressively reduced the TC of the composite. In turn, 0.10% CNT incorporation did not result in significant TC gains. The yield stress and viscosity of the mixes progressively increased as CNTs content and AR increased, by up to 119% compared with plain cement paste. No significant differences were observed in 28-day compressive strength with 0.05% CNT incorporation, while 0.10% CNT led to slight strength reductions for some mixes. Regarding flexural strength, 0.05% incorporation of either CNT decreased the strength of the mixes while 0.10% incorporation generally compensated this reduction, except for the lowest aspect ratio. Overall, CNTs with intermediate AR (around 250) was effective in improving the thermal conductivity of cement paste, increasing it by 15% with relatively low content (0.05%) while did not significantly impair the fresh and mechanical performance of the composite.

Effects of silica fume, latex, methylcellulose, and carbon fibers on the thermal conductivity and specific heat of cement paste

Study on thermal conductivity of cement with thermal conductive materials in geothermal well

Thermal conductivity plays a significant role in controlling thermal cracking of cement-based materials. In this study, the thermal conductivity of cement paste at an early age was measured by the hot plate method. The test results showed that the thermal conductivity of cement paste decreased with the increase of water/cement ratio and curing age. Meanwhile, a multiphase model for the thermal conductivity of cement paste was proposed and used to study the influence of saturation and curing temperature on the thermal conductivity of cement paste. To determine the parameters involved in this model, the thermal conductivity of each phase in cement paste was calculated by the molecular dynamic simulation method, and the hydration of cement was simulated by the Virtual Cement and Concrete Testing Laboratory. The inversion results showed that the relative error between experimental and simulation results lay between 1.1% and 6.5%. The thermal conductivity of paste in the saturated condition was 14.9–32.3% higher than that in the dry state. With the curing temperature increasing from 10 °C to 60 °C, the thermal conductivity of cement paste decreased by 3.9–4.9% depending on the water/cement ratio.

The objective of this paper is to evaluate the effect of silica aerogel on the thermal conductivity of cement paste for the construction of concrete buildings in sustainable cities. Samples consisting of Ordinary Portland Cement (OPC), free water and different volumes of silica aerogel were prepared and cured for three (3), seven (7) and 28 days. Compressive strength tests were performed on samples at three (3), seven (7) and 28 days of curing. Porosity and thermal conductivity tests were conducted on samples at 28 days of curing. The lowest thermal conductivity measured was 0.076 W/mK, which was achieved by sample mix with 20 ml of silica aerogel (M20), which represents a 93.58% reduction in thermal conductivity relative to the control mix. The highest permeable porosity measured for cement paste incorporated with silica aerogel was 25.6%, which was also obtained by sample M20. However, the highest compressive strength measured was 54.33 MPa, which was obtained by sample mix with 10 ml of silica aerogel (M10) at 28 days of curing. The addition of silica aerogel as filler in cement paste can reduce the thermal conductivity of cement paste at the expense of reduced compressive strength and increased permeable porosity.

Based on the CemData18 thermodynamic database, Gem-Selektor v3.3 (Gems) software and Matlab were used to establish a hydration model for low-heat Portland (LHP) cement. Matlab was used to create a simulation program for LHP cement hydration, and for calculating permeability and thermal conductivity based on fractal theory. The research results showed that water/cement (w/c) ratio, curing temperature and hydration time are important factors affecting the hydration of LHP cement. The larger the w/c ratio, the fewer hydration products produced in the cement paste, the looser the skeleton of the cement paste, the higher the porosity and the lower the thermal conductivity. It was also find that the higher the w/c ratio, the higher the permeability of the LHP cement paste, and that the influence of curing temperature on the thermal conductivity of cement paste is mainly reflected in the early stage of hydration.

Thermo-mechanical properties of sand and high volume mineral admixtures

Increased usage of air-conditioners in buildings leads to higher levels of electricity and energy consumption. Thermal insulation improves energyefficiency of buildings by retarding heat flow through building envelopes and thus reducing indoor cooling load. This research investigates the potential of two cement replacement materials, which are silica fume and Microwave Incinerated Rice Husk Ash (MIRHA), incorporated in cement paste as thermal insulation. Samples of cement paste with varying volumes of silica fume and MIRHA were prepared and evaluated on their thermal conductivity values. Their viability as building materials were then evaluated by measuring their permeable porosities and compressive strengths at three (3), seven (7) and 28 days of curing. Results show that higher dosage of silica fume and MIRHA in cement paste lead to lower thermal conductivity but negatively affect compressive strength and permeable porosity. MIRHA reduces thermal conductivity more efficiently than silica fume but leads to a faster decline in compressive strength and increase in permeable porosity. The lowest thermal conductivity value obtained in this experiment was 0.4273 WmK, which was achieved by samples with MIRHA incorporated at 25% of cement paste volume.

ABSTRACTThis study aimed to investigate the effect of poly(vinyl alcohol) (PVA) polymer on the thermal, mechanical, and surface properties on cementitious composites for sustainable development. Thermal properties of the PVA‐modified cement paste, including thermal insulation and energy absorption ability, were first studied and correlated with the porosity and microstructures. The experimental results indicated that the thermal conductivity of cement paste can be greatly reduced by 42.9% with 2.0 wt % addition of PVA due to the more porous structure. However, at the same time, more thermal energy can be captured and concentrated at the surface of cement paste with the increasing amount of PVA, causing an increased thermal load and a negative effect on thermal insulating efficiency of cement paste. The contradictory effect of PVA on thermal properties of cement paste should be balanced before it is used as a foaming modifier to fabricate cementitious composites with thermal insulation. In addition, the contact angle measurement revealed that PVA can be used as an effective additive to improve the hydrophobicity of cement‐based materials. Only 3.0% PVA can turn the surface nature from hydrophilicity to hydrophobicity for cement paste, which benefited to the development of self‐cleaning cementitious composites. Finally, the mechanical properties of the PVA‐modified cement paste, especially for the tensile strength that has been rarely reported, were investigated and correlated with its thermal and surface properties. Due to the compensative effects of irregular packing, formation of PVA films and microcracks, tensile strength of cement paste can be improved by 23.5% with a small scarifying of the compressive strength by adding 2.0% of PVA. In conclusion, the PVA‐modified cement‐based materials with lower thermal conductivity, hydrophobic surface nature and enhanced mechanical properties have a great potential to satisfy the high requirements in developing sustainable infrastructure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46177.

Thermal conductivity of cementitious composites containing microencapsulated phase change materials

Environmental considerations and technical benefits have directed research towards reducing cement clinker content in concrete, and one of the best ways to do this is to replace cement with supplementary cementitious materials. High calcium fly ash, ladle furnace slag, and limestone filler were investigated as supplementary cementitious materials in cement pastes, and binary mixtures were produced at 10%, 20%, and 30% cement replacement rates for each material. The water requirement for maximum packing and for normal consistency were obtained for each paste, and strength development was determined at 3, 7, 28, and 90 days for the 20% replacement rate. Furthermore, two ternary mixtures at 30% cement replacement were also prepared for maximum packing density and tested for compressive strength development. The results showed that high calcium fly ash decreased cement paste packing and increased water demand but contributed to strength development through reactivity. Ladle furnace slag and limestone filler, on the other hand, were less reactive and seemed to contribute to strength development through the filler effect. The ternary paste with 70% cement, 20% high calcium fly ash, and 10% limestone filler showed equivalent strength development to that of the reference cement paste.

Eco-efficient high performance white concrete incorporating waste glass powder

Large amounts of glass and limestone wastes are accumulating all over the world. Disposal of Limestone Powder Waste (LPW) and Waste Glass Powder (WGP) is a rapidly growing problem for some municipalities, so research for alternative utilization of these disposals is needed. In this respect, the objectives of this study are to investigate both physical and mechanical properties of samples containing LPW–WGP combinations for producing as new building brick material. An experimental approach to develop a new brick material including mainly LPW, a small quantity of Portland cement and WGP is presented. The LPW, WGP and cement are mixed, humidified and compacted under high pressure in the moulds. The values of compressive strength, flexural strength, unit weight, water absorption, abrasion resistance, freezing–thawing (F-T) resistance and thermal conductivity satisfy the relevant international standards and introduces smoother surface compared to the current concrete bricks in the market. The process undertaken can easily be applied within the current brick plants. The WGP used in LPW remarkably improves the compressive strength, flexural strength, modulus of elasticity, abrasion resistance, F-T resistance, and thermal conductivity of LPW brick samples produced in this study. The test results indicate that the samples containing LPW–WGP combinations provide better results for a potential of producing economical new brick materials.