Performance of micro and nano engineered high volume fly ash cement composite

Fly ash, a byproduct of coal-fired thermal power plants is considered an environmental pollutant if it is to be disposed of and requires considerate financial liabilities on fly ash producers for its safe disposal. But fortunately, because of its physical and chemical properties, it has found applications in many fields; like mineral extraction, soil stabilization, waste treatment and as a supplementary cementitious material. As cement industry is responsible for 5-7% of global greenhouse gas emissions, application of fly ash as a cement replacement material provides the dual benefit of cutting down the greenhouse gas emissions and in increasing the utilization rate of fly ash produced worldwide. The majority of global fly ash production falls under class F low calcium category, which has low reactivity. Therefore to improve the performance of fly ash blended cement composites, the researchers have looked at many ways like; reducing the particle size, making use of hydrated lime, silica fume, and Metakaolin, etc. Recently, the use of nanomaterials has been gaining widespread attention of the research community due to their small particle size and high reactivity that help in improving the properties of the concrete at the nanoscale level. The majority of the past research on low calcium, class F fly ash cement composites, concentrated on 60% or less of fly ash content and there is a great potential for the further improvement in replacement levels. Therefore, our research aimed at developing a cement composite that not only increases the percentage of fly ash content but also considerably increases the cement replacement level having comparable mechanical properties to that of ordinary portland cement (OPC). Based on the review of existing literature, there appeared to be no research available that investigates the effect of micro (silica fume) and nano silica in combination with hydrated lime and set accelerator on high volume fly ash (HVFA) cement composite replacing 80% of cement. Therefore, our first study was undertaken to fill up this knowledge gap. The fly ash used in this study was micronised using Sturtevant jet mill microniser to produce ultra fine fly ash (UFFA). The research findings show that when UFFA is partially replaced with silica fume (SF) and used in combination with both the set accelerator (SA) and hydrated lime (HL), there is a considerable improvement in its pozzolanic activity resulting in large improvement in its 7 and 28 day compressive strength. On the contrary, nano silica (nS) modified HV-UFFA performed better when used without the SA and HL, resulting in significantly improving its 7 and 28 day compressive strength. The strength achieved at 28 days was at par with that of OPC. The addition of SA and HL to nS modified HV-UFFA blend resulted in the development of high early age microcracking, thereby considerably reducing its 28 day strength compared to that of nS, HV-UFFA and OPC blend not containing HL and SA. The second experiment was planned to look at the effect of different concentrations of nS on raw HVFA cement blends with and without SA and HL, replacing 70% of cement. The difference in experiment 2 compared to experiment 1 were (i) raw fly ash was used in experiment 2 in lieu of UFFA as micronising fly ash consumes electricity that adds to the carbon footprint (ii) two concentrations of nano silica were used i.e. 5 and 7.5% to study the effect of increase in nano silica content on HVFA cement composite. The fly ash content was partially replaced with 5 and 7.5% of nS and 5% HL. The results show that the 7 day strength increased with the increasing amount of nano silica. However, at 28 days both the samples showed approximately the similar improvement in strength. With the addition of set accelerator to nano silica modified HVFA cement blends, there was a considerable reduction in 7 and 28 day compressive strength results. Addition of HL to HVFA cement blend, containing 5% nS showed no effect on its further strength development. However, when HL was added to the 7.5% nS modified HVFA cement coposite, a considerable reduction in its 7 and 28 day compressive strength results were observed. This shows that nS is highly effective in improving the strength of HVFA cement composites when used alone without any additives, but when it is used in combination with either HL or SA, shows no or negative effect on the development of compressive strength of raw fly ash blended cement composites. Looking at the significant improvement in the strength results of HVFA cement composites by incorporating nano silica, the next experiment was planned to looking at the effect of other nano materials on HVFA cement composites. As the major elemental oxides present in OPC are SiO2, CaO and Al2O3. This experiment was planned to incorporate the nano sized sources of these elemental oxides. Since the reaction of pure CaO is highly thermal in nature and addition of nano CaO would have been highly exothermic and could have introduced high thermal stresses at early ages of curing, nano CaCO3 was used as a source of CaO. Therefore, the third experiment plan looked at a quantitative comparative study of the effect of 5% and 7.5% of nano silica, 2.5% and 5% of nano alumina (nA) and 2.5% and 5% of nano calcium carbonate (nCC), on the properties of HVFA cement composites, replacing 80% of cement. The results show that the addition of nS significantly improves the compressive strength of HVFA cement composites and considerably increases the formation and thermal stability of silica-rich hydrogarnet phase, which increases with the increase in nS content. The addition of nCC to HVFA cement composite does not show any effect on the pozzolanic reaction at 7 days of curing but at 28 days considerably improves its pozzolanic reaction, which increases with the increase in nCC content. The performance of nCC in improving the mechanical properties is less pronounced than that of nS. The addition of nA though improves the hydration/pozzolanic reaction of HVFA cement composite, resulting in the improvement in compressive strength, but only if added in small quantities (2.5% or less). If it is added in higher amounts, it promotes the formation of Al(OH)3 gel that severely inhibits the hydration/pozzolanic reaction within the cement matrix. Based on the knowledge gained from the previous experiments, we found that the amorphous nano silica holds a great potential for the development of zero cement composite. That motivated us to design our fourth experiment, replacing 100% of cement. In the fourth experiment we replaced OPC with slag, which is another industrial by product. Zero cement mix designs were developed incorporating slag, HVFA and various concentrations of nano silica and hydrated lime. The results show that the optimum content of nano silica in a high volume fly ash, slag and HL blend is 5%. With a further increase in nano silica content although the pozzolanic reaction and the resulting C-S-H/C-A-S-H gel formation increases but it also increase the micro-cracking within the cement matrix, resulting in negatively impacting the strength development. The portlandite added externally in the form of Ca(OH)2 powder, to the nS modified SCM blend, activates the pozzolanic reaction which increases with the increase in portlandite content. The best mix design containing 5% nS, 70% FA and 25% slag in combination with 15% HL as an additive, achieved a 28 day compressive strength of 70% compared to that of OPC. It is to be noted that though this research aimed at minimising the carbon footprint of the cement composites, it was not completely eliminated. The various raw materials that have CO2 emissions associated with their production are listed below: Nano silica – As per the information provided by the supplier of Nano silica, it was produced by pyrogenic method, which is highly energy intensive process. It is produced from the flame hydrolysis of silicon tetrachloride (SiCl4) at ~1800 °C temperature. Calcium hydroxide – Calcium hydroxide is produced commercially by treating lime (CaO) with water (H2O). The CaO used in this process is produced by the de-carbonation of limestone (CaCO3), which releases CO2 into the atmosphere during production. Ultrafine fly ash (UFFA) – Though fly ash is a by-product of thermal power plants using coal as a fuel, micronizing the fly ash (i.e. reducing the particle size of the raw fly ash) is an energy intensive process. The Sturtevant jet mill microniser used to reduce the particle size of the raw fly ash runs on electricity which otherwise is produced primarily by the thermal power plants in Australia

Some aspects of the nature and incidence of stuttering among Indian primary school children in Durban.

Thesis (M.A.)-University of Natal, Durban, 1971.Stuttering has been a complex problem ever since the early history of man. It has been found to exist in some cultures to a greater extent than in others. In certain primitive cultures the phenomenon of stuttering was reported to be unknown, yet when members of these cultures were influenced by western environments some incidence of stuttering occurred among them. The influence of the environment therefore cannot be disregarded when considering causes of stuttering. Although much research has been done by speech pathologists among various world cultures they have by no means completed their task for there are many groups, living in a variety of societies, which are yet to be studied. The present rudimentary investigation into stuttering among Indians living in Durban may be regarded as a contribution to the knowledge that has already been accumulated

Drying shrinkage properties of expanded polystyrene (EPS) lightweight aggregate concrete: A review

Expanded polystyrene (EPS) is currently being utilized in sustainable materials owing to its ultra-low density and superior thermal performance. It can be incorporated in concrete mixtures to replace coarse aggregate to produce lightweight aggregate concrete (LWAC). Concerning the high shrinkage development in LWAC, the present study reviews the available published articles regarding the drying shrinkage of lightweight concretes containing expanded polystyrene. According to the previous studies, the drying shrinkage development in expanded polystyrene concrete (EPSC) has been reported to be greater than that in conventional concrete, which must be considered for its application in the construction industry. It is mainly attributed to the low elastic modulus and mechanical properties of the EPS. However, incorporating additives and fibers can improve its shrinkage resistance properties. A comprehensive comparison of drying shrinkage magnitude between various LWAC showed that the drying shrinkage strain of EPSC is not generally higher than other types of LWAC; however, the density of EPSC was measured lower than that in other types of lightweight aggregate concretes.publishedVersio

Durability of Mortar Incorporating Ferronickel Slag Aggregate and Supplementary Cementitious Materials Subjected to Wet–Dry Cycles

This paper presents the strength and durability of cement mortars using 0–100% ferronickel slag (FNS) as replacement of natural sand and 30% fly ash or ground granulated blast furnace slag (GGBFS) as cement replacement. The maximum mortar compressive strength was achieved with 50% sand replacement by FNS. Durability was evaluated by the changes in compressive strength and mass of mortar specimens after 28 cycles of alternate wetting at 23 °C and drying at 110 °C. Strength loss increased by the increase of FNS content with marginal increases in the mass loss. Though a maximum strength loss of up to 26% was observed, the values were only 3–9% for 25–100% FNS contents in the mixtures containing 30% fly ash. The XRD data showed that the pozzolanic reaction of fly ash helped to reduce the strength loss caused by wet–dry cycles. Overall, the volume of permeable voids (VPV) and performance in wet–dry cycles for 50% FNS and 30% fly ash were better than those for 100% OPC and natural sand

Nano reinforced cement paste composite with functionalized graphene and pristine graphene nanoplatelets

This study examines and compares the workability, hydration, mechanical, microstructure and transport properties of cement paste composites containing the three forms of graphene-based 2D nanomaterials synthesised from epigenetic graphite deposit, namely, graphene oxide (GO), reduced graphene oxide (rGO), and pristine graphene nanoplatelates (G). Graphene materials were used from 0.01% to 0.16% of cement weight. The rGO and G were treated with salt and surfactant, respectively during synthesis, to improve dispersion in water. Characteristics and physical strength vary among GO, rGO and G, which have influenced the properties of nano reinforced graphene-cement composites (GCCs). The 28-day compressive and flexural strength of graphene (GO, rGO and G) cement composite improved by 28% and 81%, 30% and 84%, and 39% and 38%, respectively, compared to the control mix (cement paste without graphene materials). Finally, microscopic analysis, dynamic vapour sorption (DVS), electrical resistivity and water sorptivity results suggested that graphene materials densify and reinforce the composite microstructure

Effect of clay addition to sand on organic matter retention

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Department of Agricultural Sciences, School of Life Sciences, Faculty of Science, Technology and Engineering, La Trobe University, Bundoora

Data for: Practical Rubber Pre-treatment Approch for Concrete Use – An Experimental Study

XRD of raw material: X-ray diffractograms of general blended cement, pure sodium sulfate, crumb rubber and crumb rubber soaked in 5% sodium sulfate solution XRD of hardened cement pastes: X-ray diffractograms general blended cement and the one modified with 5% sodium sulfate solution at 7 and 28 days of curin

Effects of Different Rates of Ca(2+) Addition on Respiration and Sorption of Water-Extractable Organic C to a Vertisol Subsoil

It is well known that calcium (Ca²⁺) plays an important role in binding organic matter to clay. However, most previous studies were conducted with either topsoil or pure aluminosilicates. Less is known about the effect of Ca²⁺ on binding of organic matter to clay-rich subsoils, which have lower organic-matter contents than topsoils, and their clays are more strongly weathered than pure aluminosilicates. Two experiments were conducted with a Vertisol subsoil (69% clay): a laboratory incubation and a batch sorption. The mineral substrate in the incubation experiment was pure sand alone or sand amended with 300 g clay kg⁻¹. Powdered calcium sulfate (CaSO4) at rates of 0, 5, 10, and 15 g Ca kg⁻¹ and mature wheat residue at a rate of 20 g kg⁻¹ were added to this mineral substrate and the water content was adjusted to 70% of water-holding capacity. Carbon dioxide release was measured for 28 days. Cumulative respiration per g soil organic carbon (C) (SOC from clay and residues) was increased by clay addition. Increasing Ca²⁺ addition rate decreased cumulative respiration in the sand with clay but had no effect on respiration in the pure sand. Clay and Ca²⁺ addition had no significant effect on microbial biomass carbon (MBC) per g SOC but clay addition reduced the concentration of potassium sulfate (K2SO4)–extractable C per g SOC. For the batch sorption experiment, the subsoil was mixed with 0 to 15 g Ca kg⁻¹ and water-extractable organic C (WEOC) derived from mature wheat straw was added at 0, 1485, 3267, and 5099 mg WEOC kg⁻¹. Increasing Ca²⁺ addition rate increased sorption of WEOC, particularly at the greatest concentration of WEOC added, and decreased desorption. This study confirmed the importance of Ca²⁺ in binding organic matter to clay and suggests that Ca²⁺ addition to clay-rich subsoils could be used to increase their organic C sequestration.P. Roychand and P. Marschne