Durability and leach-ability evaluation of K-based geopolymer concrete in real environmental conditions

Abstract

Geopolymer Concrete (GPC) as an alternative to Portland Cement Concrete (PCC) is a cement-less and green construction material which is produced by mixing industrial by-products with an alkaline solution. In this study, PCC and Potassium-based (K-based) GPC synthesized with 50 % fly-ash and 50 % bottom-ash were exposed to the real environmental conditions to evaluate their chemical metals leach-ability and durability over 150 and 240 days of exposure respectively. The mix contained potassium hydroxide concentration of 12 molarity, potassium silicate/potassium hydroxide ratio of 1.47, alkaline solution/ashes (fly-ash and bottom-ash) ratio of 0.54 and total aggregate content of 1800 kg/m3. To develop GPC, two methods of curing (steam curing and dry curing) were used to increase the compressive strength of GPC. According to the result of compression test, the compressive strength of steam-cured GPC increased 3.5 times when temperature elevated from ambient temperature (̴10 °C) to 80 °C. While, an increase in compressive strength of dry-cured GPC samples was 2.3 times. Non-Destructive Tests (NDT)s including Schmidt hammer, ultrasonic pulse velocity and resonant frequency test were employed to measure the relative dynamic modulus of elasticity. In this study, paver block has been selected as an application since to the best of our knowledge, there is no work reported the effect of real environmental conditions on leach-ability and mechanical properties of K-based GPC paver blocks. Two areas were paved with a total of 150 GPC and 210 PCC paver blocks. The results of the NDTs in area 1 show that the average velocity and compressive strength of GPC decreased approximately 11.6 % and 23.4 % respectively. While, the average velocity and compressive strength of PCC decreased about 8.3 % and 8.2 % respectively. In area 2, the average rate of velocity and compressive strength loss of GPC was about 12.03 % and 19.51 % respectively. Whereas, maximum decrease in average velocity and compressive strength of PCC over 240 days of exposure was 5.28 % and 9.65 % respectively. Leach-ability of GPC as another innovative aspect of current study was also measured using HACH strips since the release of heavy metals can be a concern in GPC. The results indicate that due to the heat-treatment of GPC paver blocks, all the parameters including total alkalinity, total hardness, pH, total chlorine, phosphate, copper, ammonia, iron, nitrate and nitrite were within the standard domain and were constant over 150 days of exposure. The relative dynamic modulus of elasticity power function model and exponential function model were established to find a suitable damage predictive model for both types of concrete. It was concluded that due to the higher values of Adj.R2 for both GPC (0.96) and PCC (0.92), the power function relationship compared well with the exponential function.