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

An empirical approach for the optimisation of aggregate combinations for self-compacting concrete

The fresh and hardened properties of self-compacting concrete (SCC) depend on number of factors such as paste composition, paste content, aggregate content, aggregate gradation etc. In the present investigation, the influence of the packing density of aggregates on the properties of SCC was evaluated. Experiments were conducted to measure the packing density for different combinations of aggregates precisely. A ternary packing diagram (TPD) was developed based on the packing density of measured and interpolated data. Considering the limitations in generalising the TPD and the difficulty involved in adopting mathematical models for aggregates, an attempt was made to establish a simple method for the selection of the combination of aggregates resulting in maximum packing density from the particle size distribution of aggregates (represented by the Coefficient of uniformity-C (u)). Further, studies were extended to investigate the effect of aggregate packing density on fresh and hardened SCC properties. The results indicate that for a constant paste volume and paste composition, with increase in packing density of aggregates, the fresh properties and the compressive strength of SCC were improved positively. An attempt was also made to identify the influence of 10 different proportions of aggregates having the same packing density on the properties of SCC. The results indicate that at the same aggregate packing density, the fresh concrete properties were influenced significantly by the choice of the aggregate combination, while there was little or no influence on the hardened properties. Furthermore, the experimental data obtained was used for supplementary validation of the existing model (compressible packing model) for predicting the packing density and the fresh behaviour of SCC

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

Design of propping schemes of 60-storey reinforced concrete building: a case study

A study of a 60-storey reinforced concrete residential building was undertaken to evaluate the propping schemes supporting the flat slabs. Relevant data necessary for evaluation were acquired from the construction site. Based on the obtained data, a simple methodology to formulate the alternative propping schemes is presented in this paper. The propping scheme designed at the construction site for a 10 d slab cycle is analysed and possible alternative schemes are proposed. The primary objectives of the alternative schemes are to ensure safety and economy, and to minimise the number of construction activities on each level. A comparison of the propping schemes suitable for different slab cycle durations was also performed. It is shown that specific slab cycle durations are comparatively more cost-effective

A circular framework for the valorisation of sugar industry wastes: Review on the industrial symbiosis between sugar, construction and energy industries

This paper provides a comprehensive review of literature on the properties of sugar industry waste, their varied uses in energy and construction sector, performance and limitations. An efficient upcycling of sugar industry waste in energy production would help the energy sector to reduce its dependency on non-renewable fossil fuels. Literature demonstrates that in the recent years there has been an increased research interest in thermochemical conversion of sugarcane bagasse to produce cleaner energy, rather than its landfilling or combustion. On the other hand, utilisation of secondary by-products from sugar industry in the production of cement, bricks, paver blocks, activated binder and other construction products helps to cut down the carbon footprint of the construction industry, while improving the properties of the final products. From the perspective of the sugar industry, such an arrangement eliminates disposal problems and creates additional revenue. Although independent research studies investigating the use of sugar industry by-products exist, few studies consider these valorisation options together to minimise waste and to create an efficient material flow chain. This study identifies various material and energy recovery pathways from published literature and connects the materials and processes to form a continuous material supply chain with minimum wastage. From the findings, a symbiotic framework has been developed with primary and secondary by-products from the sugar industry serving as source materials for energy production and sustainable construction products. (C) 2018 Elsevier Ltd. All rights reserved

Percolation Time and Rigidification Rate of Cementitious Suspensions

The stability and structural buildup of concrete can be evaluated by understanding the nature of the corresponding cementitious suspension using the small-amplitude oscillatory shear (SAOS) test through the time of percolation and rigidification rate, respectively. In the present study, four different cementitious suspensions—namely, 100% ordinary portland cement (OPC), OPC with 70% replacement of slag, OPC with 25% replacement of fly ash (FA), and OPC with 8% replacement of microsilica (MS)—were inves-tigated. From the results, for OPC-based suspensions, the perco-lation time decreases for increasing dosages of high-range water-reducing admixture (HRWRA) at low water-binder ratios (w/b) due to their high reactivity. In contrast, the suspensions with FA and MS exhibit a higher time for the formation of the elastic network, leading to a higher time of percolation. Further, it was identified that the suspensions with slag have the highest affinity toward the HRWRA, resulting in higher dispersion and therefore higher time required for the formation of the initial elastic network. This confirms that the dispersion and reactivity of the particles in suspensions dictate the stability and the structuralbuildup