A Study on Groundnut Husk Ash (GHA)–Concrete under Acid Attack
This paper presents the findings of an investigation on the compressive strength of Groundnut Husk Ash (GHA)-Concrete and its resistance to acid attack. The GHA used was obtained by controlled burning of groundnut husk to a temperature of 600 o C and sieved through 75 µm sieve after allowing cooingl. The compressive strength of GHA-Concrete was investigated at replacement levels of 0, 5, 10, 20, 30 and 40 %, respectively by weight of cement. A total of ninety 150 mm cubes of GHA-Concrete grade
... GHA-Concrete grade 20 were tested for compressive strength at 3, 7, 28, 60 and 90 days of curing and the microstructure of GHA-Concrete samples at 0 and 10 % replacements were examined at 28 and 90 days of curing. Also, thirty six 100 mm cubes were subjected to attack from 10 % concentration of diluted solution of sulphuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ), respectively. The result of the investigations showed that the compressive strength of concrete decreased with increase in GHA content. However 10 % replacement with GHA was considered as optimum for structural concrete. GHA provided a less compact microstructure of concrete at 28 and 90 days curing compared to OPC concrete as a result of low pozzolanic activity. The use of GHA in concrete improved its resistance against sulphuric acid, but not against nitric acid attack. The average weight loss of GHA concrete after 28 days of subjection in sulphuric acid and nitric acid were 16.3 % and 17.3 %, respectively as opposed to 22.4 % and 15.1 %, respectively for plain Portland cement concrete. Effect of Acids on GHA-Concrete The effect of 10 % concentration of sulphuric acid (H 2 SO 4 ) and nitric acid, respectively on GHA-Concrete shown in terms of weight retained, in Figures 7 and 8 , showed that concrete with GHA offered better resistance to deterioration by H 2 SO 4 than Portland cement concrete, while plain Portland cement concrete performed better than GHA concrete in a nitric acid medium. The average weight loss of GHA concrete after 28 days of immersion in sulphuric acid and nitric acid were 16.3 % and 17.3 %, respectively as opposed to 22.4 % and 15.1 %, respectively for plain Portland cement concrete. The enhanced resistance of GHA-Concrete to Sulphuric acid could be due to depletion in the Ca(OH) 2 content released from the hydration process and consumed in the GHA pozzolanic reaction, with less Ca(OH) 2 left to react with Sulphuric acid or due to less C 3 A available to form the more disruptive ettringite in the GHA-Concrete, as well as noted in  , the calcium sulphate salt formed from the chemical reaction is less soluble in water when compared to calcium nitrate, and this accounts for better resistance of the concrete to Sulphuric acid even though it is a very strong acid. On the other hand, the poor resistance of GHA-Concrete to nitric acid attack when compared with plain OPC concrete could be attributed to incomplete pozzolanic reaction of GHA after 28 days curing in water, as  reported that the replacement of OPC by a pozzolanic material usually has beneficial effect on cement durability at ages up to 1.5 years. Also, pozzolanic reaction usually reduces the Ca(OH) 2 available for reaction with acids, but GHA with a high content of CaO (13.19 %) may produce additional Ca(OH) 2 for reaction with HNO 3 to produce aqueous calcium nitrate salt which is deleterious in concrete. The high content of K 2 O (38.80 %) in GHA may also be a source of disruption in GHA-Concrete as K 2 O react with HNO 3 to produce potassium nitrate salt with adverse effect on the concrete. It was noted that 10 % concentration of solution of Sulphuric and nitric acids were very aggressive media with significant detrimental effect on GHA-Concrete grade 20. The results have also shown that Sulphuric acid (H 2 SO 4 ) is more aggressive to plain Portland cement concrete than Nitric acid (HNO 3 ), while GHA-Concrete was more resistant to sulphuric acid than nitric acid. Figure 7: Weight of GHA-Concrete immersed in H 2 SO 4 medium.