Porosity can be defined as a ratio of pore volume (volume occupied bythe fluid) to total volume of concrete. Porosity in concrete is important to bestudied; especially for materials of seaside buildings and buildings attaching theground. Salt water containing sulfate and chloride can press the pores of concreteso that concrete cracks into loose flakes and its strength reduces. An increase inporosity is thought to associate with a reduced strength of post-burnt concrete.Research was conducted to study the compressive strength, splitting tensile andporosity of post-burnt concrete using cylinders of 150 mm diameter and 300 mmhigh. Burning of samples was carried out after 28 days of age. The burning wasstarted at an oven temperature of 34 º C until it reached a maximum temperature of± 800 º C achieved at minute of 180 and then it held on for another 20 minutes, sothat the burning process lasted for 200 minutes. The test results showed that theincrease in porosity of concrete is proportional to the volume of concrete that hadhot penetration with temperature 400-800 oC. The porosity of concrete increased by20.695%, which resulted in the decrease of compressive strength and splittingtensile strength by 53.665% and 49.641% respectively.
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