Ángel Di Maio

Use of recycled fine aggregate in concretes with durable requirements

The use of construction waste materials as aggregates for concrete production is highly attractive compared to the use of non-renewable natural resources, promoting environmental protection and allowing the development of a new raw material. Several countries have recommendations for the use of recycled coarse aggregate in structural concrete, whereas the use of the fine fraction is limited because it may produce significant changes in some properties of concrete. However, during the last decade the use of recycled fine aggregates (RFA) has achieved a great international interest, mainly because of economic implications related to the shortage of natural sands suitable for the production of concrete, besides to allow an integral use of this type of waste. In this study, the durable behaviour of structural concretes made with different percentage of RFA (0%, 20%, and 30%) is evaluated. Different properties related to the durability of concretes such as absorption, sorptivity, water penetration under pressure, and carbonation are determined. In addition, the results of compressive strength, static modulus of elasticity and drying shrinkage are presented. The obtained results indicate that the recycled concretes have a suitable resistant and durable behaviour, according to the limits indicated by different international codes for structural concrete.

Recycled Concretes Made with Waste Ready-Mix Concrete as Coarse Aggregate

Using waste materials for new products is a global trend undergoing rapid development. Recycling materials allows for a more efficient life cycle and contributes to environmental protection. In the construction field, this trend has gained importance because of the shortage of natural resources and because of environmental problems caused by storing building-demolition wastes. This situation has led to the search for new applications for these wastes, and their use as aggregates in concrete is an interesting alternative. In this paper, some characteristics of recycled coarse aggregates obtained by crushing waste ready-mix concrete, as well as the mechanical and durability properties of recycled concretes made by using 25, 50, and 75% of these aggregates, are presented. Recycled concretes show lower compressive strength than conventional concrete for the higher strength level, whereas the durability properties of the two are similar.

Time Evolution of Chloride Penetration in Blended Cement Concrete

Blended cement concrete is currently a necessity to reduce environmental impacts in the construction industry. The lower clinker content may affect some durable characteristics of concrete, such as the resistance to chloride ingress. Conversely, mineral admixtures may present pozzolanic activity that improves concrete performance over time. This paper presents results of chloride ingress in concrete specimens made with slag and limestone filler blended portland cement (BPC) when located in the marine environment. Parameters including 2 water-cement ratios (w/c), 3 curing treatments, and 2 maximum aggregate sizes were analyzed. Water-soluble and total chloride ingress profiles were determined during an exposure period of 3 years. The results allowed the time evolution of both the surface chloride content and diffusivity of BPC concrete to be assessed by natural mechanisms.

Evaluation of concrete quality. Lateral Pressures test

Abstract The use of Non Destructive Teste (NDT) in concrete quality control of the “in situ” material is each time more frequent. This paper presents studies realized to stabilish the perfomance of a new NDT called Lateral Pressures when concrete strength estimation is desired. Concretes of different characteristics (strength level, aggregates type, shape and surface texture, cure conditions, etc.) are analyzed.