Critical Grain Size of Fine Aggregates in the View of the Rheology of Mortar

The aim of this research was to investigate the validity of the Krieger-Dougherty model as a quantitative model to predict the viscosity of mortar depending on various aggregate sizes. The Krieger-Dougherty model reportedly predicted the viscosity of a suspension, which includes cement-based materials. Concrete or mortar incorporates natural resources, such as sand and gravel, referred to as aggregates, which can make up as much as 80% of the mixture by volume. Cement paste is a suspending medium at fresh state and then becomes a binder to link the aggregate after its hydration. Both the viscosity of the suspending medium and the characteristics of the aggregates, therefore, control the viscosity of the cement-based materials. In this research, various sizes and gradations of fine aggregate samples were prepared. Workability and rheological properties were measured using fresh-state mortar samples and incorporating the various-sized fine aggregates. Yield stress and viscosity measurements were obtained by using a rheometer. Based on the packing density of each fine aggregate sample, the viscosity of the mortar was predicted with the Krieger-Dougherty model. In addition, further adjustments were made to determine the water absorption of fine aggregates and was transferred from successful experiment to simulation for more accurate prediction. It was also determined that both yield stress and viscosity increase when the fine aggregate mean size decreases throughout the mix. However, when the mean size of the fine aggregates is bigger than 0.7 mm, the yield stress is not affected by the size of the fine aggregate. Additionally, if aggregate grains get smaller up to 0.3 mm, their water absorption is critical to the rheological behavior

Studies on strength and weight loss of paper concrete

Huge amounts of waste paper are discarded every year, of which only a minute fraction is recycled and the rest is dumped in landfills. Paper fibres can only be recycled a limited number of times before they become too short or weak to make high-quality recycled paper. This eventually adds to the amount of waste paper being generated and not recycled. It would thus be advantageous to use this waste as a low-cost sustainable construction material and make it a value-added product. In this study, Portland pozzolana cement (fly ash based), waste newsprint paper and water were used to prepare paper concrete cubes. Initially, investigations were performed to determine the optimum soaking time required for softening the paper fibres of the newsprint paper. The study mainly addressed the strength and weight loss of the paper concrete cubes with age. The results indicate that, at 28 d, the paper concrete lost 25-50% of its initial weight and a maximum cubic compressive strength of 5.40 MPa was obtained

Onset and intensity of shear thickening in cementitious suspensions – A parametrical study

Understanding the intensity and onset of the shear thickening behaviour for cementitious suspensions is of prime importance in high shear processes like mixing and pumping of concrete in construction. In the present study, the onset and intensity of shear thickening of cementitious suspensions were investigated by a parametrical approach (water binder ratio (w/b), high range water reducer (HRWR) dosage, mineral admixture, shear rate) using an appropriate rheological protocol. Results show that, among the mineral admixtures, the suspension with ground granulated blast furnace slag (GGBS) features the highest shear thickening intensity and the earliest onset of shear thickening with respect to HRWR dosage. Moreover, this investigation shows that, among all the investigated parameters, the HRWR dosage influences the intensity and onset of shear thickening profoundly