International Concrete Abstracts Portal

One of the most important challenges for the cement industry is to find sustainable solutions to mitigate environmental footprint of its activities. Geopolymers are particularly attractive for this purpose; the use of waste as precursors, along with a room temperature curing, makes these materials low-polluting binders potentially suitable for sustainable building products. The lack of information on effective admixtures is limiting the practical acceptance of geopolymer concrete. The purpose of this paper is to study the influence of different superplasticizers, commonly used in Portland cement concrete technology, on properties of fly-ash based geopolymers. First, second and third generation superplasticizers (i.e., lignin-, naphthalene-, melamine-, polycarboxylic ether, acrylic based superplasticizers) have been used for the preparation of pastes and mortars. Two different amounts of admixture were tested: 0.6wt% and 1.0wt% by mass of binder. Among the investigated admixtures, the polycarboxylic ether based superplasticizer is the most effective. With a dosage of 1.0wt % by mass of fly ash it can be achieved an increase in workability of both geopolymer pastes and mortars without compromising the final strength of hardened material.

Bottom ash produced by burning municipal solid wastes in incinerators (MSWI) has been proposed as a mineral addition for concrete but removing the metals is still an open issue. A new process has been recently developed to completely eliminate the aluminum particles through a mechanical process. In this way the negative side-effect consisting in the formation of gaseous hydrogen due to the reaction between the aluminum and the calcium hydroxide produced by portland cement hydration is prevented. The new process also includes a special wet-grinding phase to increase the fineness of ground bottom ash (GBA), to the advantage of its pozzolanic activity. At the end of this process, GBA is used in the form of slurry (40-50% of solid content) to partly replace portland cement. In this research project, GBA with a maximum size of 5 µm (200■10^-6 in) was used in light-weight, self-compacting concretes (SCC) containing expanded clay as coarse aggregate with a maximum size of 16 mm (0,64in). All the mixtures were manufactured with a shrinkage-reducing admixture (SRA) and a CaO-based expansive agent to significantly reduce the drying shrinkage in a low RH (55%) environment. A polycarboxylate-based superplasticizer (with 30% of active polymer) was adequately dosed in order to manufacture SCCs at a given water/(cement +cementitious material) ratio of 0.37±0.02 . Moreover, the influence of steel fibers on the tensile and flexural strength as well as on ductility has been investigated. Similar concretes for freezing-thawing exposure classes including an air-entraining agent (to guarantee an air content close to 4% by volume) were investigated. The research has been carried out using the funding objective POR Regional Competitiveness and Employment part of the European Regional Development Fund 2007-2013 - Action 1.1.2

In the 21st century, climate change is a fundamental threat to the human species due to our collective inability to reduce carbon emissions and slow the pace of climate change. Mounting evidence predicts increased frequency and severity in future environmental climate-related events leading to potential disaster scenarios. In addition to designing buildings and infrastructure to minimum life safety provisions, adoption of fortification measures against climate-related, natural and manmade disasters must occur. Enhancing the robustness, durability, longevity, disaster resistance, and safety of structures is accomplishable with innovative materials and technology, sound construction practices, and employment of appropriate inspection and maintenance strategies. The safety, serviceability and extended service life minimizing the risk of failure for buildings and infrastructure can be ensured through sustainable and resilient design, construction and maintenance.

Cement production accounts for 1650 million metric tons of yearly global CO2 emissions [1], making it one of the largest contributors to worldwide CO2 emissions. One pathway to reducing CO2 emissions associated with concrete construction is through the use of alternative cementitious materials and binders (ACMs) such as calcium sulfoaluminate, calcium aluminate, and alkali-activated binders. These materials often require lower production temperatures than ordinary portland cements (OPC) and have lower calcium contents, reducing the emissions associated with CO2 released from calcium carbonate during calcination. Most ACMs are not new materials, but past uses have been primarily limited to small-scale applications such as pavement repairs and little field experience exists concerning their long-term durability in highly-trafficked structures such as pavements and bridge decks. This paper presents outcomes after the first year of a U.S. Department of Transportation effort to increase understanding of how to best utilize ACMs in new transportation infrastructure throughout the U.S. and presents the challenges in evaluating the durability of these materials using laboratory testing methods developed for use with OPC concrete. These concepts form the foundation for continued research and broader implementation of ACMs in transportation infrastructure.

A novel technique to upgrade the mortar durability by surface coating layer formation and densification using an electrodeposition method is suggested here. In this technique, the SiO32- ions as key raw materials are applied. Under the applied electric field, they are transported into the pores to react with Ca(OH)2 to promote the additional C-S-H gel formation, which induces the densification of mortar. Besides, the accelerated hydrolytic reaction of SiO32- ions, and the reaction of SiO32- ions in the outer electrolyte with the leached Ca2+ promote C-S-H/silica gel precipitation on the mortar surface. Furthermore, by a comparative experiment, it has been found that this technique can moderately increase the compressive strength and flexural strength of electrodeposited mortar sample. Also, the chloride diffusion into the electrodeposited mortar sample is notably decreased, which demonstrates the effectiveness of this electrodeposition technique in upgrading the durability.