Several studies have been pursued in Japan on developing concrete using high volume blast-furnace slag cement for reducing CO2 emissions arising from calcination of cement. However, when using high volume blast-furnace slag cement, various problems are encountered, such as decreased fluidity retention ability caused by the reduction of admixture dosage and decreased strength enhancement. In this paper, the authors focus on the adsorption properties of polycarboxylate ether superplasticizers and the properties of hardened concrete that incorporates a component of high volume blast-furnace slag cement, and discuss the development of a new type of superplasticizer through molecular design and optimization of the admixture composition. The admixture improved the fluidity and properties of hardened concrete using slag cement containing more than 60% blast-furnace slag.

In this study, the polycarboxylate superplasticizers (PCs) with solid content up to 80% were synthetized using special redox initiator at 318K. In the radical polymerization reactions, combining with Fourier Transform Infrared Spectroscopy (FTIR) and Gel Permeation Chromatograph (GPC), the initiator dosing dosage, reaction temperature, reaction time and the concentration of system in the copolymerization reaction were systematic investigated through orthogonal design experiments. The performances of new PCs in cement paste were tested by measuring the fluidity and fluidity retention. The slump and the compressive strengths of concrete were also determined. Compared with traditional PC, the new PC has a better advantage in workability of fresh concrete and mechanical properties of hardened concrete.

In this research several fiber-reinforced mortars (FRMs) were studied. The effectiveness of three different kinds of macro-fibers was tested: brass-coated steel fibers (SF), polyvinyl-alcohol fibers (PM and anti-crack HP glass fibers (GF) were separately added to superplasticized mortar mixtures, at the same rate of about 1,2% by volume of the mortar. Moreover, special FRMs were also manufactured combining a CaO-based expansive agent with a shrinkage reducing admixture (SRA) in order to reduce the risk of cracking induced by drying shrinkage and make more reliable mortars from the durability point of view. All the mortar mixtures were characterized by the same w/c ratio of 0.45, and the same sand/cement ratio of 3.0, as well as the same amount of a polycarboxylate-based superplasticizer (0.6% by weight of cement). A control superplasticized mixture (CM) with the same w/c, the same sand/cement ratio, but without fibers, expansive agent and SRA was also prepared and studied for comparison purpose. Moreover, an expansive mortar (EM) without fibers but with expansive agent and SRA was manufactured and studied. All the mortar mixtures were characterized for the workability in the fresh state (where they showed approximately the same plastic consistency), and in the hardened state by measuring compressive and flexural strength, as well as free or restrained length changes. The results obtained show the effectiveness in the restraint expansion of the combined use of macro-fibers, expansive agent and SRA when glass fibers and steel fibers were used.

Polysaccharides modify the rheological properties of cement based systems. Depending upon their chemistry, molecular architecture, and adsorption tendency, they have different modes of action. Some polysaccharides like diutan gum have strong effect on the fluid phase; others like starch strongly interact with particles. This paper presents effects of diutan gum and starches in presence of polycarboxylates. Rheometric investigations with varied particle volume fractions and increasing coarse aggregate diameters were conducted. The results show that starches have stronger influence on the rheology at high particle volume fractions than diutan gum. At lower particle volume fractions this trend is inverted. Experiments with aggregates sizes up to 16 mm (0.63 in.) indicate that stabilizing agent influences on the effects of aggregates on yield stress were small; however up to 1.0 mm (0.04 in.), a significant effect on the plastic viscosity could be observed, which levelled off at larger diameters.

Water desorption from superabsorbent polymers (SAP) into cement-based pastes was characterized by neutron radiography imaging to promote the understanding of the mechanisms behind internal curing of concrete. Two anionic SAP samples were used which differed in their inherent sorption kinetics in cement pore solution (SAP 1: self-releasing; SAP 2: retentive). Portland cement pastes with W/C of 0.25 and 0.50 and a paste additionally containing silica fume (W/C = 0.42, SF/C = 1/10) were investigated. Desorption from SAP 1 initiated immediately. SAP 2 released water into all the matrices as well, even in the cement paste with the high W/C of 0.50. In the other two pastes, which require internal curing by principle, SAP 2 retained its stored liquid for as long as the dormant period of cement hydration. Intense desorption then set in and continued throughout the acceleration period and even beyond. These findings explain the pronouncedly higher efficiency of SAP 2 as an internal curing admixture when compared to SAP 1.