Recycling of demolished concrete is an effective method for reducing construction waste. Recycled fine aggregate includes a large quantity of hydrated cement paste. The cement paste influences qualities of recycled fine aggregate, and, in turn, the properties of concrete containing recycled fine aggregate. As a result, concrete containing recycled fine aggregate has lower strength and durability than concrete with natural aggregate. However, the manner in which the quality of recycled fine aggregate influences the properties of concrete remains unclear. When considering the use of recycled concrete for construction, the durability of concrete with recycled fine aggregate must be investigated. The purpose of this study is to determine the influence of the quality of recycled aggregate on the properties of concrete at W/C ranging from 0.25 to 0.7. The parameters investigated to evaluate durability are strength, pore volume, shrinkage, carbonation, and resistance to frost damage. The results show that water absorbed by the aggregate migrates to paste around particles of aggregate, and influences the volume of water and pores in paste. Therefore, when recycled fine aggregate with high water absorption is used in concrete, shrinkage and volume of gas permeating into concrete increase, and durability lowers.

This paper presents a comparative study on the water permeability and chloride penetration in lightweight and normalweight aggregate concrete (LC and NC). Water-cementitious material ratios (w/cm) of 0.35 and 0.55, and silica fume content of 0% and 10% as cement replacement were used to obtain concrete with different strength levels. In concrete mixture proportioning, the volume of the coarse aggregate for the lightweight concrete was the same as that in the corresponding normalweight concrete. The results indicated that at the strength level of 30-40 MPa, the water permeability of the LC with a w/cm of 0.55 was lower than that of the NC with equivalent w/cm when subjected to 4 MPa water pressure. However, at a w/cm of 0.35 the water permeability of LC and NC was not significantly different. The resistance of the LC to chloride ion penetration was similar to that of the corresponding NC with the same w/cm and mixture proportion. As the LC had lower compressive strength than that of the corresponding NC, the results indicated that the LC would probably have lower water permeability and better resistance to the chloride-ion penetration than the NC with equivalent 28-day compressive strength.

Early age cracking may be what is commonly known as "plastic shrinkage cracking", which normally is cracking of horizontal surface before and during setting (initial phase), and "thermal cracking" which normally is in the period of cooling following the period of temperature rise due to heat of hydration (thermo phase). In the initial phase, any mix water absorption by the LWA (i.e. like in concretes with relatively dry LWA) may contribute to increased settlement, capillary tension of pore water and shrinkage, and thus, an increased risk of cracking in typically the first hour after finishing. However, in the early hardening age the absorbed water may constitute a reservoir which contributes to swelling of the paste which counteract any plastic shrinkage and/or any contraction due to cooling, and thus, to reduced risk of cracking. In the thermo phase the temperature rise in LWAC is potentially higher due to the lower heat capacity of the LWA, which may result in larger contraction during cooling, which again may generate higher stress, and finally to higher risk of cracking. On the other hand the autogenous shrinkage is significantly reduced or even eliminated, and the E-modulus is lower, which both contributes to lower stress, and thus, to lower risk of cracking. The net result is often reduced risk of early age cracking.

The Ontario Ministry of Transportation has a mandate to specify cost-effective methods and materials for the construction and maintenance of provincial highway structures. In support of this mandate, the Bridge Durability Work Group initiated a performance evaluation of epoxy-coated reinforcement (ECR) in the Ontario bridge environment. Findings of the investigation, which are summarized in this report, strongly indicate that the long-term performance of the ECR is not likely to provide the corrosion resistance or associated maintenance free service life that was originally anticipated by the ministry. Several Ministry structures constructed with ECR have already been rehabilitated, before achieving even a 20-year service life. The paper details the results of numerous in house field investigations to assess the condition of ECR in-service in typical Ontario highway bridges. The paper also presents the findings of field and research studies carried out by independent consultants and academics on behalf of the ministry, to examine ECR performance and to recommend alternative approaches for corrosion protection and structure condition assessment.

This paper deals with a numerical modeling of concrete carbonation, based upon durability indicators (DIs), within the framework of a durability approach. Firstly, the methodology and the selected panel of universal DIs concerning carbonation are presented. Secondly, with the purpose of protecting structures against carbonation-induced corrosion, a model accounting for the coupled CO2-H2O-ionic transports, the carbonation reactions of Ca(OH)2 and C-S-H, the pH decrease, and the microstructure evolution is described. In this model, the DIs porosity, initial Ca(OH)2 content, and liquid water permeability are introduced as major input data. Complementary parameters are also used: Ca(OH)2 crystal size, C-S-H content and capillary pressure curve. The main numerical outputs are the carbonation kinetics, the residual Ca(OH)2 and newly formed CaCO3 content profiles, and the pH value. As a first step, the model is validated with accelerated carbonation data obtained on a cement paste and on three porous concretes. The carbonation depth and profiles, measured by means of phenolphthalein spray test and thermal analysis respectively, are in good agreement with the numerical simulations. The study is completed by a sensitivity analysis. The model, together with the test methods required for the assessment of the relevant DIs, could be included in a toolkit for durability evaluation and prediction of carbonation-induced corrosion of real structures.