The degradation of concrete sewer pipes by sulphuric acid attack is a problem of global scope, resulting in substantial economic losses each year. In this study, five admixtures, which offer a range of potential improvement mechanisms, were used at various dosages to enhance the resistance of concrete made with Type 50E cement to chemical sulphuric acid attack. The resistance to sulphuric acid of concrete specimens incorporating these admixtures was measured and compared to that of control specimens. An attempt was made to determine whether there is a relationship between the effect of the various admixtures on mechanical strength and porosity and the resistance of concrete to H₂SO₄ attack. Results indicate that metakaolin reduced the mass loss of concrete specimens due to immersion for eight weeks in H₂SO₄ solutions having concentrations of 7% and 3% (by volume) by 38 and 25%, respectively, compared with that of the control specimens. Other admixtures (OCI, Caltite and Xypex) reduced the mass loss of concrete specimens in the range 12–20% for the 7% H₂SO₄ solution and in the range 9–16% for the 3% H₂SO₄ solution. Although silica fume effectively increased compressive strength and reduced the porosity of concrete, its contribution to the resistance of concrete to chemical sulphuric acid was minor. No clear relationship could be established between the mechanical and physical properties of concrete (compressive strength and porosity) and its resistance to sulphuric acid attack. It was also found that the decline in compressive strength of concrete specimens subjected to H₂SO₄ attack was directly proportional to their mass loss, following a linear relationship.

Corrosion of concrete sewer pipes by sulfuric acid attack is a problem of global scope, leading to multibillion dollar losses each year. However, research is still needed to better understand the mechanisms of sulfuric acid attack on concrete and the related effects of concrete mixture design parameters. In this paper, the combined effect of wetting-drying cycles and concrete mixture design parameters including cement content, water/cement (w/c) ratio, and coarse aggregate content on the resistance of concrete to sulfuric acid was investigated. Specimens from various concrete mixtures were soaked in sulfuric acid solutions with pH of 0.3, 0.6, 1.0, 1.5, 2.0, 2.5, and 3.0. The mass loss of concrete specimens due to immersion in sulfuric acid and wetting-drying cycles was used as a measure of concrete degradation. For specimens that experienced no mass loss due to low concentration of sulfuric acid, the thickness of the gypsum layer that formed on specimens’ surface was measured on thin sections using trans...

The effect of geopolymer cement on the compressive strength and resistance to sulphuric acid of concrete made with type 10 and type 50E cements was studied. Hydration products and microstructure of various concrete mixtures incorporating geopolymer cement were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmitted light microscopy in order to identify the mechanisms underlying the effects of the geopolymer cement on concrete properties. Experimental results indicate that using geopolymer cement as partial replacement for ordinary Portland cement (OPC) effectively improved both the compressive strength and resistance to sulphuric acid. Replacement of 50% OPC by geopolymer cement increased the 28-day compressive strength by about 50% and reduced the mass loss of concrete specimens subjected to eight weeks of immersion in sulphuric acid solutions with pH of 0·3 and 0·6 by 42% and 30%, respectively. The effect of geopolymer cement on the compressive strength and sulphuric acid resistance of concrete made with type 50E cement was less significant than that for concrete made with type 10 cement. Results of XRD, SEM and light microscopy indicate that improvements in compressive strength and sulphuric acid resistance of the geopolymer modified concrete can be mainly attributed to the formation of new hydration products such as calcium–magnesium–aluminium-oxide silicates. A direct relationship between the ability of geopolymer modified concrete specimens to resist sulphuric acid and their normal 28-day compressive strength was found, but varied with the binder used.

Hydrogen sulfide is a serious problem for many municipalities across North America and worldwide. Odor, safety, and corrosion are the major problems associated with the presence of hydrogen sulfide in sewerage systems. This paper investigates the effect on sulfide generation of using innovative coatings in concrete sewer pipes. A pilot-scale model, consisting of three concrete pipes (each 75 cm in length and 30 cm in internal diameter), was used to simulate the process of sulfide generation in a sewer system. Two of the pipes were internally coated with either cuprous oxide (C.O) or silver oxide (S.O), while the third one served as a control. Each of the oxides was mixed with a commercial epoxy, used for repairing concrete sewer pipes, prior to spraying on the internal surface of the concrete pipe specimens to form a coating film. Test data showed that the sulfide generation by sulfate-reducing bacteria (SRB) in the C.O and S.O coated pipes was reduced by 92% and 100%, respectively, compared with that of the control pipe. The coating films effectively decreased the bacterial count in the nutrient solution. Results also suggested that the slime layer formed in the C.O coated pipe was significantly smaller and thinner compared with that of the control pipe. No slime layer was observed on the internal surface of the S.O coated pipe at the conclusion of the test.

Microbiologically induced corrosion is a leading cause of the deterioration of wastewater collection, transmission and treatment infrastructure around the world. This paper examines the feasibility of using artificial neural networks (ANNs) to predict the compressive strength of concrete and its degradation under exposure to sulphuric acid of various concentrations. A database incorporating 78 concrete mixtures performed by the authors was developed to train and test the ANN models. Data were arranged in a patterned format in such a manner that each pattern contains input variables (concrete mixture parameters) and the corresponding output vector (weight loss of concrete by H₂SO₄ attack and compressive strength at different ages). Results show that the ANN model I successfully predicted the weight loss of concrete specimens subjected to sulphuric acid attack, not only for mixtures used in the training process, but also for new mixtures unfamiliar to the ANN model designed within the practical range of the input parameters used in the training process. Root-mean-squared error (RMSE) and average absolute error (AAE) for ANN predictions of weight loss due to sulphuric acid attack were 0.013 and 8.45%, respectively. The ANN model II accurately predicted the compressive strength of the various concrete mixtures at different ages with RMSE and AAE of 2.35 MPa and 4.49%, respectively. A parametric study shows that both models I and II can successfully capture the sensitivity of output variables to changes in input parameters.

Each year billions of dollars are spent around the world on the rehabilitation and/or replacement of concrete sewer pipes damaged by sulfuric acid corrosion. This paper reports the findings of an extensive experimental program undertaken to evaluate the resistance of 17 different concrete mix designs with different additives and w/c ratios to sulfuric acid attack. Silica fume, Metakaolin and Organic Corrosion Inhibitors (OCI) in different concentrations were added to the cement to improve the resistance of the concrete paste to sulfuric acid attack. The weight loss of the concrete samples immersed in two concentrations of sulfuric acid (3% and 7%) was measured to evaluate the degree of concrete degradation. The effect of the various admixtures on the compressive strength and porosity of the concrete samples were also evaluated in an effort to determine the relationships between these attributes and the resistance of the concrete samples to a sulfuric acid attack. Data from a two months exposure test showed that the addition of Metakaolin or OCI to the concrete mix resulted in a significant improvement in the concrete resistance to sulfuric acid attack compared to the control mix. Silica fume treated concrete exhibited little or no improvement compared to the control mix. The data also showed that the compressive strength and porosity of the concrete provide little guidance if any to the resistance of the concrete paste to sulfuric acids attack.