Measuring Thermal Mass of Sustainable Concrete Mixes

Abstract

Nowadays, the popularity of sustainable concrete construction is increasing every passing year. The purpose of the construction industry is to increase the life of the residence by lowering Co2 emissions and to increase the use of natural resources. Examination of thermal mass can be used to prevent or minimize temperature swings in the building and can be used to eliminate the need for energy consumption. Thermal mass reduces the risk of overheating in the summer and provides passive heating in the winter. Thermal mass is currently evaluated with “admittance” that is the ability of the element to exchange heat with the environment and is based on specific heat capacity, thermal conductivity and density. The aim of this study is to evaluate the effect of thermal properties namely, density, specific heat capacity and thermal conductivity on thermal mass of concrete. In order to evaluate the effect of such; thermal properties, different types of cement materials (PFA, GGBS, and SF) and various types of aggregates (NA and RCA) are used. Additionally, water-cement ratio is investigated. Once thermal properties are found, thermal dynamic properties are calculated theoretically for each sample. These calculations lead an understanding on the effects of different types of cement materials, recycled coarse aggregate and water-cement ratio of the concrete mixes on the thermal admittance and hence thermal mass. The laboratory tests results were analysed that PFA content concrete mixes were decreased the thermal conductivity more than other type of cements content mixes (such as SF and GGBS).30% PFA content in concrete mix has greater reduction thermal conductivity of the concrete mix. on the other hand, 15 % SF was decreased the thermal conductivity equal percentage (6.5%) with 55% GGBS content concrete mix. The laboratory results are shown that 10 and 20% SF content concrete has greater specific heat capacity than 10 and 20% PFA content concrete. 65% GGBS content concrete mix has greatest specific heat capacity of the concrete mix than all of the mixes. When 30% natural aggregate is replaced by recycled coarse aggregate, the concrete mixes have more lightly. It means that the concrete mixes are less dense than NA concrete. mixes. From the test results, the recycled coarse aggregate are affected thermal prOperties of concrete mixes more than the different types of cements content concrete mixes. RCA content concrete mixes have greater specific heat capacity value than NA content concrete mixes. However, GGBS content was greater than SF and PFA content in the concrete. The lowest decrease in the specific heat capacity is obtained as 3.9 % by using 100 % PC with 30 % RCA content concrete mix (C5). Whereas, when the w/c ratio minimized such as in the GGBS concrete mix (C2), the specific heat capacity is decreased by 14.8 % that results in the highest decrease in specific heat capacity in all the mixes. The results are defined that when minimizing water - cement ratio is applied in the concrete; the thermal diffusivity of the concrete is improved. Thermal admittance value is affected by thermal conductivity, density and the specific heat capacity of the concrete mix. When GGBS is used in concrete mix; it increases the thermal admittance more than all groups. PFA content in concrete mixes have the lowest thermal admittance value than all mixes. Silica Fume concretes has similar value of thermal admittance with Portland cement concrete mixes. RCA content in concrete mixes have the lowest thermal admittance values than other natural aggregate content in concrete mixes. Thermal admittance does not need to have high or low thermal conductivity of concrete mix. The importance is to have a moderate thermal conductivity. The results are provided that thermal admittance is increased with high specific heat capacity, high density and moderate thermal conductivity of the concrete mixes. Those factors are vital for improving thermal admittance of concrete mix.