Evaluation of Partially Degraded Existing Sewer System : Inspection of Cement Concrete Pipe

Abstract

International audienceThe laboratory of civil engineering (LGCGM) at INSA Rennes, France, has performed several studies on the durability of cement mortar in several environments. The objective of the present study is to examine the effective state of concrete of Rennes sewer system. The age of those systems can reach and exceed 50 years. During this time, the aggressive environment has evolved: often public buildings have replaced industrial zone, permeability decrease of soils... Such mechanicals and chemicals solicitations induce internal and external damage of concrete pipes. Our investigations, based on SEM micro graphs, X-ray diffractions and micro analysis, were carried out on different samples: some of them suffering hard deterioration and the other with no apparent signs of damage. Simultaneously, mechanical properties were studied: compressive strength, Brazilian test, determination of the depth of reduced alkalinity with phenolphthalein on freshly fractured surface. Those analyses are completed with porosity and capillarity measurements. That experimental analysis showed that the interior deterioration was principally due to the expansive salt gypsum but carbonation is also present: importance of the two phenomena is correlated with the porosity of the mortar. In some cases alkali reaction is present. The formation of a gypsum surface deposit in the sulphuric acid environment creates a layer susceptible to abrasion and removed easily. Consequently, the damage increase rapidly. An exterior deterioration is also observed and is correlated with the soil (carbonation, chlorite, mechanical flexure)