Jorge de Brito

Concrete Made with Coarse Concrete Aggregate: Influence of Curing on Durability

This article will present the results of experiments conducted to determine the influence of different curing conditions on the durability of recycled aggregate concrete (RAC) made with coarse crushed concrete. Four different curing conditions that represent a wide range of quality control production were tested. The curing conditions tested ranged from uncontrolled outer environment conditions to standard defined temperature humidity curing conditions. The properties analyzed were shrinkage, water absorption by immersion and capillarity, carbonation, and chloride penetration. The article concludes that RAC is affected by curing conditions in much the same way as conventional concrete.

Construction and demolition waste indicators

The construction industry is one of the biggest and most active sectors of the European Union (EU), consuming more raw materials and energy than any other economic activity. Furthermore, construction waste is the commonest waste produced in the EU. Current EU legislation sets out to implement construction and demolition waste (CDW) prevention and recycling measures. However it lacks tools to accelerate the development of a sector as bound by tradition as the building industry. The main objective of the present study was to determine indicators to estimate the amount of CDW generated on site both globally and by waste stream. CDW generation was estimated for six specific sectors: new residential construction, new non-residential construction, residential demolition, non-residential demolition, residential refurbishment, and non-residential refurbishment. The data needed to develop the indicators was collected through an exhaustive survey of previous international studies. The indicators determined suggest that the average composition of waste generated on site is mostly concrete and ceramic materials. Specifically for new residential and new non-residential construction the production of concrete waste in buildings with a reinforced concrete structure lies between 17.8 and 32.9 kg m−2 and between 18.3 and 40.1 kg m−2, respectively. For the residential and non-residential demolition sectors the production of this waste stream in buildings with a reinforced concrete structure varies from 492 to 840 kg m−2 and from 401 to 768 kg/m−2, respectively. For the residential and non-residential refurbishment sectors the production of concrete waste in buildings lies between 18.9 and 45.9 kg/m−2 and between 18.9 and 191.2 kg/m−2, respectively.

Using fine recycled concrete aggregate for mortar production

This research assessed the performance of mortars in which recycled concrete aggregates (RCA) was a component. It replaced natural sand but kept the same particle size distribution. Three mortars were produced with replacement ratios of 20%, 50% and 100% as well as a reference mortar containing no recycled aggregate. The compressive and flexural strength, water absorption by capillarity, drying capacity and susceptibility to cracking of these mortars were analyzed first. Then, based on these results, the most satisfactory replacement ratio was chosen and the following properties were analyzed: water retentivity, shrinkage, adhesive strength, modulus of elasticity, and water vapor permeability. Somewhat surprisingly the best results in the first stage occurred for 20% and 100% replacement ratios, leading to a cautious choice of the 20% ratio for the second stage. Generally the mortar with 20% replacement ratio performed better than the reference mortar, except for adhesive strength and dimensional stability.

Use of recycled aggregates from construction and demolition waste in geotechnical applications: A literature review

The use of recycled aggregates (RA) in construction constitutes a significant step towards a more sustainable society and also creates a new market opportunity to be exploited. In recent years, several case-studies have emerged in which RA were used in Geotechnical applications, such as filling materials and in unbound pavement layers. This paper presents a review of the most important physical properties of different types of RA and their comparison with natural aggregates (NA), and how these properties affect their hydraulic and mechanical behaviour when compacted. Specifically, the effects of compaction on grading size distribution curves and density are analysed, as well as the consequences of particle crushing on the resilient modulus, CBR and permeability. The paper also contains an analysis of the influence of incorporating different RA types on the performance of unbound road pavement layers as compared with those built with NA by means of the International Roughness Index and deflection values. The results collected from the literature indicate that the performance of most RA is comparable to that of NA and can be used in unbound pavement layers or in other applications requiring compaction.

Limit States and Service Life of Cement Renders on Façades

The research presented in this paper is related to the durability of cement renders on facades, based on fieldwork data relative to the condition and extent of degradation of 100 facades of residential buildings in Portugal. Deterioration paths are obtained for staining, cracking, and detachment that show the loss of performance of the facade over time until a critical minimum acceptance level is reached, which is considered an estimated durability limit. These degradation patterns are analyzed individually to confirm whether any of three types of defects can effectively be considered limit states for the durability of cement renders on facades. The combined effect of all the defects that occur is also modeled as a single degradation path, and the expected service life is quantified. The results confirm that detachment constitutes a limit state of cement-rendered facades because it directly affects the physical durability of renders. Staining and cracking alone do not generally tend to signal the end of t...

Durability of Concrete with Recycled Coarse Aggregates: Influence of Superplasticizers

AbstractThe use of recycled aggregates in concrete production can significantly contribute to its sustainability, but it may also jeopardize its durability. The use of superplasticizers may compensate for this performance handicap by contributing to the improvement of the inner structure of this type of concrete. The main goal of this study is to evaluate the effect of standard and high-performance superplasticizers on the key durability-related properties (shrinkage, water absorption by immersion and by capillarity, carbonation and chloride penetration resistance) of concrete made with different percentages of recycled coarse aggregates (RCA) from crushed concrete and compare the findings with the corresponding effect on conventional concrete. The overall conclusion is that recycled aggregate concrete is more susceptible to deterioration because of environmental conditions affecting this concrete’s durability performance more than that of conventional concrete. However, introducing superplasticizers in r...

Environmental analysis of a construction and demolition waste recycling plant in Portugal Part I: Energy consumption and CO2 emissions

This work is a part of a wider study involving the economic and environmental implications of managing construction and demolition waste (CDW), focused on the operation of a large scale CDW recycling plant. This plant, to be operated in the Lisbon Metropolitan Area (including the Setúbal peninsula), is analysed for a 60 year period, using primary energy consumption and CO2eq emission impact factors as environmental impact performance indicators. Simplified estimation methods are used to calculate industrial equipment incorporated, and the operation and transport related impacts. Material recycling--sorted materials sent to other industries, to act as input--is taken into account by discounting the impacts related to industrial processes no longer needed. This first part focuses on calculating the selected impact factors for a base case scenario (with a 350 tonnes/h installed capacity), while a sensitivity analysis is provided in part two. Overall, a 60 year global primary energy consumption of 71.4 thousand toe (tonne of oil equivalent) and a total CO2eq emission of 135.4 thousand tonnes are expected. Under this operating regime, around 563 thousand toe and 1465 thousand tonnes CO2eq could be prevented by replacing raw materials in several construction materials industries (e.g.: ferrous and non-ferrous metals, plastics, paper and cardboard).

A new method to determine the density and water absorption of fine recycled aggregates

The construction industry keeps on demanding huge quantities of natural resources, mainly minerals for mortars and concrete production. The depletion of many quarries and environmental concerns about reducing the dumping of construction and demolition waste in quarries have led to an increase in the procuring and use of recycled aggregates from this type of waste. If they are to be incorporated in concrete and mortars it is essential to know their properties to guarantee the adequate performance of the end products, in both mechanical and durability-related terms. Existing regulated tests were developed for natural aggregates, however, and several problems arise when they are applied to recycled aggregates, especially fine recycled aggregates (FRA). This paper describes the main problems encountered with these tests and proposes an alternative method to determine the density and water absorption of FRA that removes them. The use of sodium hexametaphosphate solutions in the water absorption test has proven to improve its efficiency, minimizing cohesion between particles and helping to release entrained air.

Generation of construction and demolition waste in Portugal.

In line with the growing concern around the world about construction and demolition waste (CDW) management, an attempt has been made to quantify the amount of CDW generated in Portugal, a country where no reliable/official data exist. This is an increasingly important concern of companies, businesses and municipalities involved with CDW, in a context of rising demands and more demanding recent legislation. One methodology is presented to quantify the present generation, and another to extrapolate this generation over the next few years, up to 2020. It is concluded that at present substantially less CDW is generated than the figure usually cited for Portugal, based on Spanish estimates, although it is predicted that this value will be higher on a 10-15 year timescale, reaching over 400 kg person-1 year-1.

Environmental analysis of a construction and demolition waste recycling plant in Portugal--Part II: Environmental sensitivity analysis.

Part I of this study deals with the primary energy consumption and CO(2)eq emissions of a 350 tonnes/h construction and demolition waste (CDW) recycling facility, taking into account incorporated, operation and transportation impacts. It concludes that the generated impacts are mostly concentrated in operation and transportation, and that the impacts prevented through material recycling can be up to one order of magnitude greater than those generated. However, the conditions considered for the plants operation and related transportation system may, and very likely will, vary in the near future, which will affect its environmental performance. This performance is particularly affected by the plants installed capacity, transportation fuel and input CDW mass. In spite of the variations in overall primary energy and CO(2)eq balances, the prevented impacts are always higher than the generated impacts, at least by a factor of three and maybe even as high as 16 times in particular conditions. The analysis indicates environmental performance for variations in single parameters, except for the plants capacity, which was considered to vary simultaneously with all the others. Extreme best and worst scenarios were also generated to fit the results into extreme limits.