The influence of paste quality [water-cementitious material ratio (w/cm), binder type, admixtures, etc.] on concrete properties has been extensively studied. However, there is only a few data on how the volume fraction of paste in concrete may or may not affect these properties. This paper reviews existing data on this subject. Apart from workability, most engineering properties as well as durability characteristics are not negatively affected by a reduction of the paste volume. Low paste volume concrete therefore represents an interesting option to produce economical concrete, both from ecological and economical point of view. This nevertheless requires compensating the workability loss by proper usage of admixtures. The general advantages and limitations of this approach are discussed.

The X-ray diffraction analysis and mercury intrusion porosimetry were employed to investigate the hydration process of calcium sulfoaluminate (CSA)- portland cement blends with C4A3S mass concentration, C3S/C4A3S, and CS/C4A3S mass ratios ranging from 7.7 to 22.0%, 1.0 to 6.5, and 0.5 to 1.2, respectively. Owing to the hydration of adequate C4A3S contents and the generation of sufficient quantities of expansive ettringite, blends with C4A3S amounts as well as C3S/C4A3S and CS/C4A3S values comprised between 17.6 and 22.0%, 1.0 and 1.7, 0.5 and 1.0, respectively, showed high-early strengths and low drying-shrinkage when compared to normal portland cements. The formation of expansive ettringite was associated with concentrated pore distributions and most preferred pore radii ranging from either 47 to 225 or 367 to 896 nanometers, depending on both C3S/C4A3S and CS/C4A3S ratios.

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.

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.

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.