International Concrete Abstracts Portal

The economic use of chemical admixtures depends on supply chains. Therefore, in most regions ins sub-Saharan Africa (SSA), the use of admixtures is not common practice. This amplifies the unfavorable framework for concrete construction such as fragmentary supply chains, high local cement prices, and unfavorable construction site facilities in this region significantly. The use of superplasticizer (SP) and stabilizing agents (STA) can enhance the concrete technology in SSA, since they can disassociate the concrete quality from external boundary influences. After providing a general overview of the peculiarities of the SSA boundary framework, economic concepts are provided, how existing material solutions can be significantly improved by the use of SPs and STAs based on locally available materials such as lignosulphonates and cassava starch. Finally a three step optimization process is described that helps developing flowable concrete based on materials that can be accessed in most locations in SSA.

The interaction of methoxy-capped poly(ethylene glycol) polymers (MPEG) and a poly(methacrylic acid) anionic polymer (PMA) from water onto sodium Montmorillonite (Na-Mmt) particles untreated or treated by calcium chloride was studied at 20°C. In the absence of Ca2+, MPEGs are able to intercalate by displacing the water molecules present in the interlayer space, as shown by XRD and TGA analyses. In contrast, the adsorbed amount of PMA remains low. The saturation of Mmt with Ca2+ prevents MPEG intercalation through replacing sodium by a stronger water coordinator in the interlayer space, but slightly increases PMA adsorption possibly through a calcium bonding mechanism. This was confirmed with PCE superplasticizers and Na- and Ca-saturated Mmt clays. Whatever the PCE, a larger amount was consumed on Na-Mmt than on Ca-Mmt. This confirms the occurrence of two consumption mechanisms: (i) a superficial adsorption via cation bonding of the carboxylate groups with anionic sites on clay surfaces, (ii) intercalation of ether units of the grafts in the interlayer space by displacement of water molecules coordinated to the exchangeable cations.

The composition of the aqueous solution in alkali-activated binders, i.e., the high alkalinity and the high ionic strength challenge chemists to design molecules exhibiting the same plasticizing effects as in cementitious materials. The highest difficulty probably lies in alkali-silicate activated systems due to the presence of multivalent silicate oligomers in solution. Reported here are new insights about the adsorption of polymers in presence of various concentrated electrolyte solutions in order to mimic the harsh conditions present in geopolymer pastes. In order to eliminate the problem of the reactivity of such systems, TiO2 nanoparticles were used as a model substrate. The adsorption of polymer molecules as well as the specific adsorption of monovalent and divalent ions is revealed. Those results are compared to the rheological characteristics of alkali-hydroxide or alkali-silicate activated geopolymers. The conclusions which can be drawn from the model system fit qualitatively very well with the classical slump tests done on real systems.

The calcination temperature in cement manufacturing can be reduced by the addition of sulphate and fluoride containing compounds and it is possible that sulphate and fluoride ions elute to the suspension after calcination. This paper describes the influence of sulphate and fluoride ions on the action of polycarboxylate based superplasticizer in cement paste. When the amount of K2SO4 or KF was increased, the viscosity of the cement paste with superplasticizer increased. The amount of adsorbed superplasticizer was decreased by K2SO4 addition but increased by KF addition. The fluidity with polycarboxylate based superplasticizer containing more functional groups was less affected by K2SO4 addition. In contrast to the case of K2SO4 addition, the increase in the degree of viscosity by KF addition was not dependent on the amount of functional groups. The specific surface area increased with K2SO4 or KF addition.

The objective of this study was to establish a recycling system for cement sludge by hydration control and an evaluation of the residual cement content of sludge. The adsorption behavior of sodium gluconate on cementitious materials was clarified in this study. The saturated absorption behavior between sodium gluconate and alite follows a Langmuir adsorption isotherm. The delayed hydration time depends on the concentration of residual sodium gluconate. When the residual concentration of sodium gluconate was over 0.018–0.020 mass%, cement hydration did not proceed. The relationship between the heat liberation after 1 day and the amount of non-hydrated alite as calculated by X-ray diffractometry is linear. The amount of non-hydrated alite can be estimated by using calorimetric data. Finally, the amount of non-hydrated alite in sludge water can be estimated by using calorimetric data, magnesium hydrate hexahydrate (Mg(NO3)2·6H2O).