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

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

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

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

Assessment of the Efficiency of Eco-Friendly Lightweight Concrete as Simulated Repair Material in Concrete Joints

The high production of carbon dioxide from concrete cement manufacturing and the high utilization of natural resources in concrete has been a concern for research in recent decades. Eco-friendly concrete (Eco-Con) is a type of concrete that uses less energy in its production, utilizes waste materials, produces less carbon dioxide, and is durable. This study assesses the efficiency of the proposed lightweight Eco-Con mixes with 32 MPa compressive strength in repairing different types of concrete structures. Rubber and lightweight expanded clay aggregate (LECA) were used as lightweight materials in the Eco-Con mixes. One Portland cement concrete mix (CC) and three different Eco-Con mixes, namely geopolymer rubber concrete (GR), geopolymer LECA concrete (GL), and rubber-engineered cementitious composite (RECC), were produced and compared. The concrete mixes were utilized as simulated ‘repair’ materials in several types of concrete joints, namely reinforced slab–beam joints (400 × 300 mm L-shape, 500 mm width, and 100 mm thickness) subjected to bending, concrete joints in beams (100 × 100 × 350 mm) subjected to bending, and concrete joints in unconfined and fiber-reinforced polymer (FRP) confined columns (100 mm diameter and 200 mm height) subjected to axial compression. The reinforced slab–beam joint and FRP-confined column joint were tested with two joint angles of 0° and 45°. The results indicated that RECC is an efficient lightweight Eco-Con alternative to Portland cement concrete in repairing concrete structural elements, especially beams and FRP-confined columns, as it increased their strength capacities by 43% and 190%, respectively. At the tested joint angles (0° or 45°), the use of Eco-Con mixes showed relatively lower slab–beam joint strength capacity than that of the CC mix by up to 14%. A joint angle of 45° was better than 0°, as it showed up to 7% better slab–beam joint strength capacity. Using shear connectors in slab–beam joints had adverse effects on concrete cracking and deformability

Nanosilica modified high-volume fly ash and slag cement composite: Environmentally friendly alternative to OPC

In the quest to develop a green cement composite with the lowest possible carbon footprint and the highest possible use of industrial by-products, an experimental investigation was undertaken, replacing 100% of ordinary portland cement. This paper presents the results of an experimental program to develop a zero-cement composite, incorporating 2.5, 5, and 7.5% nanosilica, 72.5, 70, and 67.5% fly ash, 25% ground granulated blast furnace slag (GGBFS), and hydrated lime used as a cement additive at 10 and 15% of the total supplementary cementitious material. Compressive strength tests were undertaken to study the mechanical properties of mortar samples of various mix designs. In addition, scanning electron microscopy, thermogravimetry, and X-ray diffraction were undertaken in conjunction with quantitative phase analysis to investigate the various physicochemical changes taking place within the cement matrix and to formulate strategies for its further development. The results demonstrate that the addition of nanosilica and hydrated lime to low calcium/high-volume fly ash and GGBFS blend can help in achieving an environmentally friendly zero-cement composite without the need of any heat treatment. The optimum content of nanosilica was found to be 5%. With the further increase in nanosilica content, although the pozzolanic reaction and the resulting C-S-H=C-A-S-H gel formation increases, it also increases the microcracking within the cement matrix, resulting in the reduction in compressive strength at both 7 and 28 days of curing. The siliceous hydrogarnet formed as a result of the pozzolanic reaction of amorphous silica (FA, GGBFS, NS), with the calcium aluminate present in GGBFS, shows very poor crystallinity with no visible peak reflection in X-ray diffraction data. The formation of siliceous hydrogarnet increases with the increase in amorphous nanosilica, but decreases with the increase in hydrated lime content

High volume fly ash cement composite modified with nano silica, hydrated lime and set accelerator

This paper presents the effect of nano silica, used individually and in combination with set accelerator or hydrated lime, on the properties of high volume fly ash (HVFA) cement composites, replacing 70 % of cement. Compressive strength test along with X-ray diffraction and thermogravimetric analysis were undertaken to study the effect of various elements on the physico-chemical behaviour and the pozzolanic activity of the blended samples. The addition of 5 % nano silica improved the 7 day strength of the blended sample by 76 % and by further increasing the nano silica content to 7.5 %, the 7 day strength increased by 94 %. However, at 28 days both 5 and 7.5 % nano silica modified samples showed approximately the similar improvement in strength i.e. 54 and 50 % respectively. With the addition of set accelerator to nano silica modified HVFA cement blend, there was a considerable reduction in both 7 and 28 day strengths. Addition of 5 % hydrated lime to HVFA blend, modified with 5 % nano silica showed no effect on the further improvement of strength. However, when 5 % hydrated lime was added to the 7.5 % nano silica modified HVFA blend, there was a considerable reduction in both 7 and 28 day strengths. This demonstrates that nano silica is highly effective in improving the strength of high volume fly ash cement blends when used alone, but when it is used in combination with either hydrated lime or set accelerator, shows no or negative effect on the development of strength

Pathway, classification and removal efficiency of microplastics in wastewater treatment plants

Microplastics (MPs) contamination in water environment has recently been documented as an emerging environmental threat due to their negative impact on the ecosystem. Their sources are many, but all of them are from synthetic materials. The sources of MPs are cosmetics and personal care products, breakdown or abrasion processes of other plastic products, textile and tyre, bitumen and road marking paints. Because of their low density and small particle size, they are easily discharged into the wastewater drainage systems. Therefore, the municipal wastewater treatment plants (WWTPs) are indicated to be the main recipients of MPs before getting discharged into the natural waterbodies. Therefore, understanding the occurrence and fate of MPs in WWTPs are of great importance towards its control. The aim of this article is to provide a comprehensive review to better understand the pathways of MPs before entering the WWTPs, characteristics of MPs in wastewater, and the removal efficiency of MPs of the existing wastewater treatment technologies adopted by the WWTPs. This review also covers the development of potential microplastics treatment technologies investigated to date. Based on the review of existing literature, it is found that the existing WWTPs are inefficient to completely remove the MPs and there is a risk that they may get discharged into the ambient water sources