A concrete cube may be allow in urea solution of pH-8 for a period of 28 days.After that we check its compressive strength,I found not satisfactory result.
Concrete don't react with urea,but surface deterioration occurs depending on the porosity, due to development of crystals within pores like frost action. Since you are maintaining constant pH 8 which leads to release of calcium from hydrated paste to balance pH of pore solution to exposed solution the strength may decrease with time. Don't put satisfactory not satisfactory put increased or decreased, or no affect etc. Provide experiment details properly and fully like w/b ratio, type of cement, duration of exposure, method of immersion, constant pH maintained through out or not etc.
with lower Ph concrete may lost its alkalinity which may leads to corrosion of steel reinforcement, this is happen only when Ph of concrete reduces to 10 or below.
its better to check the Ph value of concrete after 28 days of curing with urea solution.