Effects of aggregate types on acid corrosion attack upon fly – Ash geopolymer and Portland cement concretes – Comparative study

In this study, effects of the siliceous granite and calcareous dolomite aggregate types on the acid resistance behaviours of fly ash - geopolymer (FA - GPC) and Portland cement (PC) concretes, were investigated and compared. The granite and dolomite aggregate types used were selected as these represent extremes of excellent and poor acid resistance responses by the different rocks, respectively. For each aggregate type, PC concretes of strength levels comprising 35 MPa and 50 MPa, were prepared using CEM I 52.5R cement. Similarly, FA - GPC concretes also of about 35 MPa and 50 MPa strengths, were made using an activator comprising a mixture of sodium hydroxide and sodium silicate. PC and FA - GPC concrete cube samples of 100 mm size were cast and immersed in 10% wt. concentrations of HCl or H₂SO₄ acid solutions. Residual mass loss and residual compressive strength results of the samples were determined after 0, 28, 56 and 84 days of storage in the acid solutions. Analytical studies on acid corrosion attack upon the concretes were conducted using X - ray diffraction (XRD), petrography and scanning electron microscopy (SEM). It was found that the acid resistance behaviour of FA - GPC concretes is superior to that of corresponding PC concretes. Findings of the present study show that granites or siliceous aggregates generally, are suitable for producing acid resistant FA – GPC concretes. In contrast, calcareous aggregate types especially dolomite, are effective in reducing the progression of acid attack upon PC concretes, as these aggregates corrode along with cement paste, leading to relatively slower uniform surface wear.