<p>One of the most important properties of concrete is its strength. However, in certain circumstances, like urban sewage systems, concrete is attacked and corroded, being exposed to the sulfuric acid produced from H2S in a biological process, thereby undergoing a decrease in its strength. This paper studies the effect of concrete admixtures on surface strength of concrete in acidic environments, using Twist-Off method. In order to investigate the corrosion process in concrete and consequent decrease in its strength, the calibration curve for the partially destructive twist-off method was firstly determined. Then, 15 concrete samples mixed with air-entraining admixtures, plasticizers, and micro-silica were prepared and placed in acidic and neutral PH environments in sewer pipes and sewage treatment plant. Using twist-off method and calibration curve, surface strengths of the samples were measured in a 135-day period and compared with one another.</p>