Study of water ingress into foamed concrete

Abstract

Foamed concretes have many potential applications. The good thermal insulating properties of foamed concrete can provide thermal insulation to buildings leading to energy saving which translates not only to monetary savings but produce positive environment impact as well. Understanding and limiting the water ingress into foamed concrete is important for these applications because an increase in water content of foamed concrete can significantly increase the conductivity of foamed concrete. Low permeability material also improves the durability of the structural element. Foamed concrete with good thermal insulation and low water permeability coefficient can also have possible application in undersea pipe insulation.So far, there are limited water ingress studies done on foamed concrete as it is a relatively new material. In particular, there is a dearth of water permeability data for foamed concrete which limits the use of cellular concrete in applications where durability is a major concern. Thus, water ingress mechanism of foamed concrete is ofgreat research significance.Existing water permeability test setups have drawbacks such as specialized sample requirement, leakage around sample, trapped air voids in the test system and small quantity of flow that is difficult to measure. In view of this, a new test facilitywhere the flow of water is radial has been developed with the intention of circumventing the problem of 2-D water flow. It was able to produce consistent and reliable permeability results.The experiments consist of studying the water ingress due to capillary effect measured by water absorption and sorptivity and water ingress due to pressure flow, measured by water permeability. The parameters studied are water to cement (w/c)ratio, foam content and polymer addition. High w/c ratio increases water ingress due to capillaries and pressure effects. High foam content tends to decrease water ingress due to capillary effect but reverse trend is observed for a positive pressure gradient.This is attributed to different degree of bubble saturation in the entrained air void due to the two different mechanisms. Polymer addition improves the water resistance incement pastes but reduces water resistance in foamed concretes. The permeability of foamed concrete is dependent on the pressure of the ingress water. This is because as the pressure of the ingress water increases, the degree of saturation of the entrained airvoids increases and more water flow through this low water resistant zone. As a result,the overall permeability also increases.A computational model (FLUENT ) and an analytical model by Jacobs and Mayer (1992) were used to compare with the experimental results to study trends and to predict permeability of foamed concrete. For a foam content of less than 50% in cement pastes, the experimental value matches more closely to the predictions of FLUENT model but at higher foam content > 50%, the Jacobs and Mayer model provides more representative results.