Superplasticizer and Shrinkage Reducing Admixture Dosages for Microfine Cement in Grout Systems

Grouts have numerous applications including crack repair as maintenance in construction industries. Microfine cements are intensively used for high strength mortar and grout products. They are ideal for injection grouting in structural repair. Such grouts should have suitable rheological properties to be injectable, especially those used in repair and rehabilitation. The use of superplasticizers (SP) in these products is thus becoming increasingly crucial to achieve favorable workability and viscosity properties. A difficulty in such grouts is the plastic shrinkage due to finer particles used. It is thus necessary to determine optimum SP and shrinkage reducing admixture (SRA) dosages for a microfine cement based grout. In this study, a saturation dosage was decided from two Polycarboxylate ether (PCE) based SPs in relation to neat cement using slump flow and rheological parameters. A range of grout mixtures was formulated containing micro silica (MS) and fly ash (FA), and tested for suitable rheological and mechanical parameters. Based on the results, a grout mixture with MS and FA was selected to determine optimum SRA content. According to the results, a SP dosage of 3% by weight of neat cement is sufficient to achieve saturation. The grout material including MS and FA can produce comparable properties to neat cement grout. MS is found to improve compressive strength within the range considered, whereas a higher FA content provides favourable rheological properties. Finally, a SRA dosage of 4%, which could reduce the shrinkage by about 43% after 28d days, is determined for the grout system.

Penetrability of microfine cement grouts: experimental investigation and fuzzy regression modeling

One-dimensional injection tests were conducted on sand columns with a height of 134 cm for the penetrability evaluation of microfine cement grouts. Three ordinary cement types were pulverized to obtain microfine cements having nominal maximum grain sizes of 20 and 10 μm, and these cements were used in the present investigation. Suspensions with water to cement (W/C) ratios of 1, 2, and 3, by weight, were injected into 13 clean sands with d15 ranging from 0.17 to 2.25 mm and Cu ranging from 1.19 to 6.67. Pulverization of the ordinary cements to produce microfine cements extends the range of groutable sands to “medium-to-fine”. Cement fineness; suspension W/C ratio and apparent viscosity; and sand grain size, gradation, and relative density are very important parameters, as they substantially affect both grout penetration and maximum injection pressure. The penetration length of cement grouts was correlated to parameters pertinent to the suspension, sand, and injection process by performing fuzzy and ordinary linear regression analyses of the injection test results. The resultant fuzzy regression models provided successful penetration length predictions for the majority of the cases analyzed, while the best ordinary regression model exhibited a correlation coefficient not higher than 0.363.

Special Aspects of Hydration Process of Microfine Cement

The aim of the present research was to determine special features of hydration process of two commercial microfine cements compared to CEM I 42.5N cement with similar mineralogical composition. The influence of cement fineness and composition on the hydration process was investigated by isothermal calorimetry of cement pastes and quantitative X-ray powder diffraction of hydration products at 1, 3, 7, 14 and 28 days.