International Concrete Abstracts Portal

In portland slag cements (PSC), different slag compositions can produce variations in workability due to the disparity in the surface chemistry of the slags. Here, the surface chemistry of different PSCs dispersed in water was studied in the absence and presence of polycarboxylate (PCE) superplasticizers. Six PSCs were prepared by mixing portland cement with 30 or 70 wt.% of three slags. As PCEs, two copolymers based on methacrylic acid–co–?–methoxy poly(ethylene glycol) methacrylate ester were employed. It was found that the slags sequester ions from the pore solution, namely Ca2+ and SO42- ions forming an electrical double layer on the slag surface. Zeta potential measurements confirmed that different slags can exhibit different surface charges which can strongly affect PCE adsorption. The differences in the amounts of PCEs adsorbed result in different dosages required to achieve comparable dispersion. Generally, all slag cements tested required less PCE to achieve the same fluidity as with neat cement.

A polycarboxylate superplasticizer (PCE) with a novel star-shaped structure was prepared through copolymerization of acrylic acid (AA), isobutenyl polyethylene glycol (IPEG), and star-shaped polymerizable active center by an esterification between polyol and AA. In the first esterification step, the esterification rate reached more than 95% with the catalyst/polyol ratio of 0.07:1, inhibitor/AA ratio of 0.04:1 (or 0.011:1), water-carrying agent dosage of 70g and esterification time of 7 hours. In the second polymerization step, the highest fluidity of cement paste was achieved at the initiator/AA/IPEG ratio of 0.28: 3.3: 1. Infrared spectroscopy (IR) and 1H Nuclear magnetic resonance (1H NMR) measurements were used for structural characterization, and the spectral results confirmed the product’s star-shaped structure. Furthermore, this star-shaped PCE exhibited higher energy efficiency than the conventional comb-shaped PCE, indicated by its excellent paste fluidity and adsorption behavior in cement paste.

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.

One of the essential problems of superplasticized concrete is the loss of fluidity over time. To limit this problem one must improve the compatibility of superplasticizers and cement. This is not a trivial task as cement contains phases with different responses to superplasticizers in the first hours of hydration. In the present work, the role of the polymer structure on the flow loss over time on superplasticized cement pastes has been studied. For this, we have correlated the impact of different molecular structures on the adsorption degree and ionic solution composition with the rheological properties of fresh cement pastes. The results revealed a high excess of aluminium in the aqueous solution. This could be due to aluminum complexation by the polymer or a poisoning of ettringite growth complemented by a stabilization of nano-sized ettringite particles. In addition, except for one of the studied polymers, the flow loss seems to decrease abruptly when the concentration of carboxylate ions in solution drops below a critical value (0.7-1.2 µeq/g).

The ability to control the setting of cement can be of use in various applications such as slip forming, oil well cements, or in normal applications due to variable conditions and time constraints. Typically cement setting is controlled via set retarders or set accelerators, but rarely are the two used in combination. The combination of the two, however, can lead to increased flexibility in construction methods. In this work, we present a system in which the dormant period of cement is extended with sucrose, and then drastically reduced by adding calcium hydroxide, a phase that preferentially adsorbs sucrose. We demonstrate that increasing doses of calcium hydroxide decrease the dormant period of sucrose-retarded cement, up to a complete cancellation of retardation, which is reached at the plateau of the sucrose-calcium hydroxide adsorption isotherm.