 In contrast to the stony grey of concrete made with Portland cement, the near-white color of GGBS cement permits architects to achieve a lighter colour for exposed fair-faced concrete finishes, at no extra cost.To achieve a lighter colour finish, GGBS is usually specified at between 50% to 70% replacement levels, although levels as high as 85% can be used.GGBS cement also produces a smoother, more defect free surface, due to the fineness of the GGBS particles.