Characterization of high-volume fly-ash cement pastes for sustainable construction applications

Oven-drying as a preconditioning method for air permeability test on concrete

The process of transport of fluid flux is generally described in terms of adsorption, diffusion, absorption, and permeability. Concrete has a highly heterogeneous and complex structure; therefore, it is difficult to constitute exact models of the concrete structure from which the behavior of the material can be reliably predicted. The gel is composed of gel particles and interstitial voids, known as gel pores. Capillary pores represent the spaces not filled by solid components of the hardened cement paste; therefore, the volume and size of the capillary voids depend on the distance among unhydrated cement particles in the freshly mixed cement paste (that is, water–cement ratio) and the degree of hydration. Air voids in concrete are formed either because of entrapped air during casting, or they are intentionally entrained by using an air-entraining agent. Chemically combined water is the water that is an integral part of the structure of various cement hydration products. This water is not lost on drying; however, upon heating at elevated temperatures, the decomposition of hydrates releases it. Absorption is the process by which concrete takes in a fluid because of capillary suction in pores to fill the space within the material.

16 – Permeation Analysis

Measurements of the permeation or sorption characteristics of concrete are increasingly being used as indexes of durability or resistance to chemical attack of new concrete This investigation was intended to find if these relatively simple, inexpensive tests can be used to assess the condition of the concrete in mature structures that may have deteriorated during their service life Such structures may be nearing the end of their design life, but it may be necessary to extend their service life In such cases the state of the concrete needs to be assessed The paper explores the profiles of oxygen permeability and water sorption, with distance from the surface, of concrete taken from in-service structures typically in the 20 to 30 year age range and hence proposes generalized permeability and sorption profiles However, as the two types of measurement, permeability and sorption, do not, for concrete from in-service structures, correlate one with the other or with carbonation depth or strength, it is unli

Permeability and Sorption Properties of Mature Near-Surface Concrete

Many permeation methods for characterizing the near-surface quality of concrete claim to have the added advantage of being applicable in situ. This paper attempts to highlight some of the aspects associated with using such tests in situ, and deals specifically with experience in using the convercrete absorption test (CAT) for in-situ tests on concrete structures. Some of the better known permeation test methods are listed, and reasons are given for selecting the CAT for this investigation, in preference to other methods. Results of CAT tests performed in the laboratory on laboratory cast samples showed the CAT can be sensitive to variations in water/cement ratio and curing time, moisture content at the time of test, and surface orientation. Good correlations between covercrete absorption and other durability index parameters were obtained for the laboratory-cast samples, but these correlations were poor or even absent when applied to in-situ tests on mature concrete structures. From these tests it appears that permeation methods have little value for assessing the quality and state of durability of concrete structures.

H. Paroll

Papers

On the correlation between permeability properties and strength of concrete