International Concrete Abstracts Portal

Water entraining agent using porous aggregate known as internal curing (IC) has become an important component of high-performance concrete (HPC). This paper presents part of the experimental results of an on-going research project regarding the effectiveness of porous ceramic waste aggregates called ‘PorCera’ (PC) as IC agent for high-performance structural concrete elements. Previous studies have proven the effectiveness of both the presoaked recycled porous ceramic coarse aggregate (PCCA) as an IC and shrinkage compensating agents in reducing autogenous shrinkage of HPC. The main purpose of this study is to investigate the synergistic effect of a combination of shrinkage compensating agents and the PorCera on silica fume HPC behavior. This hybrid curing technique includes a combination of shrinkage reducing agent (SRA), expansive additive (EA), and internal curing provided by the recycled PC. Its effect on compressive and split tensile strengths, autogenous shrinkage, and internal self-stress were investigated. Results indicate that HPC mixtures made with this hybrid curing system drastically reduce the amount of autogenous shrinkage, and consequently the induced internal stress and perform much better than the single incorporation of shrinkage compensating agents.

In recent years ultra-high-performance concrete (UHPC) has gained more interest in the concrete construction industry due to the expected high durability of UHPC, as well as extended architectural opportunities. Compared to normal concrete it is possible to build filigree and lighter structures with ultra-high-performance concrete. The aim of this study was to evaluate the durability of different UHPC mixtures regarding alkali-silica reaction (ASR) and delayed-ettringite formation (DEF). UHPC prisms were exposed to different temperature and moisture conditions in a special climate simulation chamber. Scanning electron microscopy (SEM) was used to determine possible deterioration of UHPCs. Results of microscopic investigations show that products of ASR are only locally enriched. An ettringite growth was observed on microcracks (< 10 µm) in intentional pre-damaged samples or close to incompletely hydrated clinker grains. Macroscopic deteriorations due to ASR or ettringite growth could not be detected. However, steel fibers of UHPC were affected by corrosion.

This paper evaluates the strength, toughness properties and plastic shrinkage potential of the structural synthetic fiber reinforced concrete. The test results indicated that there was a significant increase in the flexural strength and a slight increase in the first crack strength as the fiber content was increased from 0.5 to 2.0% by volume. The Japanese toughness factors and equivalent flexural strengths were also significantly increased as the fiber content increased. There was also a tremendous increase in impact strength with an increase in fiber content. Very high average residual strengths (ARS) (ASTM C 1399) were obtained and the ARS values increased as the fiber content increased. The contribution of structural synthetic fibers to plastic shrinkage reduction of concrete was studied using cement-rich concrete and the experimental results are reported in this paper. The fiber dosages used were 0.5, 1.0, and 2.0% by volume of concrete. The tests were conducted using 51 mm (2.0 in.) thick slab that was 1 m (3 ft) long and 0.6 m (2 ft) wide. The crack development was enhanced by using fans that can produce a wind velocity of 22 km/h (13.2 m/h). The performance of these fibers was compared using the crack areas of control slab with no fibers and fiber reinforced slabs. The results indicate that structural synthetic fibers at the dosages used, tremendously reduced the plastic shrinkage in concrete. The crack area reduction varied from 100 to 92% of the plain concrete. There was absolutely no cracking when a fiber dosage of 2.0% by volume of concrete was used.

Geopolymer is a specialized material resulting from the reaction of a source material that is rich in silica and alumina with alkaline solution. It is essentially portland cement free concrete. This material is being studied extensively and shows promise as a greener alternative to normal portland cement concrete. It has been found that geopolymer concrete has good engineering properties with a reduced carbon footprint resulting from the total replacement of normal portland cement. The research undertaken at Curtin University of Technology has included studies on geopolymer concrete mixture proportions, structural behavior, and durability. This paper presents the results on mixture proportions development to enhance workability and strength of geopolymer concrete. The influence of factors such as: curing temperature and régime, aggregate shape, strength, moisture content, preparation and grading, and the addition of superplasticizers, on workability and strength are presented.

Heavyweight concrete made of water, cement, and heavyweight aggregate is used for shielding in structures where radiation protection is required. Water reduction helps to achieve high density mixtures, since water is the component with the lowest specific gravity. Thus, the use of superplasticizers helps to obtain workable concrete with low water-cement ratio (w/c) and high density. This paper discusses properties for heavy-weight self-consolidating concrete (SCC) made with polycarboxilic-based superplasticizer and barite aggregate. Fresh concrete properties were characterized using the suitable test methods employed in SCC. Since segregation is a key issue in this type of concrete due to the large difference between the densities of the mortar and coarse aggregate, some specific tests were carried out in concrete columns to verify homogeneity of the concrete, including the measurement of the capillarity and water permeability.