Minimum Strength Requirements Research Articles

Influence of Asphalt Emulsion Inclusion on Fly Ash/Hydrated Lime Alkali-Activated Material.

Supplementary cementitious materials have been widely used to reduce the greenhouse gas emissions caused by ordinary Portland cement (OPC), including in the construction of road bases. In addition, the use of OPC in road base stabilization is inefficient due to its moisture sensitivity and lack of flexibility. Therefore, this study investigates the effect of hybrid alkali-activated materials (H-AAM) on flexibility and water prevention when used as binders while proposing a new and sustainable material. A cationic asphalt emulsion (CAE) was applied to increase this cementless material’s resistance to moisture damage and flexibility. The physical properties and structural formation of this H-AAM, consisting of fly ash, hydrated lime, and sodium hydroxide, were examined. The results revealed that the addition of CAE decreased the material’s mechanical strength due to its hindrance of pozzolanic reactions and alkali activations. This study revealed decreases in the cementitious product’s peak in the x-ray diffraction analysis (XRD) tests and the number of tetrahedrons detected in the Fourier transform infrared spectroscopy analysis (FTIR) tests. The scanning electron microscope (SEM) images showed some signs of asphalt films surrounding hybrid alkali-activated particles and even some unreacted FA particles, indicating incomplete chemical reactions in the study material’s matrix. However, the H-AAM was still able to meet the minimum road base strength requirement of 1.72 MPa. Furthermore, the toughness and flexibility of the H-AAM were enhanced by CAE. Notably, adding 10% and 20% CAE by weight to the hybrid alkali-activated binder produced a significant advantage in terms of water absorption, which can be explained by its influence on the material’s consolidation of its matrices, resulting in significant void reductions. Hence, the outcomes of this study might reveal an opportunity for developing a new stabilizing agent for road bases with water-prevention properties and flexibility that remains faithful to the green construction material concept.

Seismic loss assessment of seismically isolated buildings designed by the procedures of ASCE/SEI 7-16

This paper investigates the seismic loss assessment of seismically isolated and non-isolated buildings with steel moment or braced frames, designed by the seismic design standard of ASCE/SEI 7-16. The seismic loss is calculated from the damage to structural and non-structural components, as well as the demolition and the collapse of buildings. This study demonstrates that the expected annual losses for seismically isolated buildings are half or less than half of those calculated for non-isolated buildings. These losses depend on the types of seismic isolation systems and seismic force resisting systems used. Among the cases of isolated buildings studied in this paper, the most cost-effective systems are found to be the buildings designed by minimum strength requirement in ASCE/SEI 7-16 and with isolators which have displacement capacity 1.5 times larger than the minimum required in ASCE/SEI 7-16, in terms of expected annual losses. This study also compares the results obtained from different approaches of selection and scaling of ground motions. The following research finds that when Incremental Dynamic Analysis approach with far-field ground motion set in FEMA P695 is used, the computed expected total annual losses become doubled from the Conditional Spectra approach.

Synthetic granulated blast furnace-like slag from bauxite residue smelting and its use in multi-component Portland composite cement

This study investigates the composition and reactivity of two GBFS-like slags produced from bauxite residue (BR). The composition of the slags was analysed using a multi method approach. The hydraulic reactivity was assessed in Portland composite cement and with the addition of anhydrite, limestone and combinations thereof. The presented approach is further discussed in the context of the full valorisation of BR and the economic as well as environmental implications. Both slags demonstrated a good strength contribution at a 25% substitution rate. Both failed the minimum strength requirements for GBFS according to EN 15167–1, using a 50% substitution rate. Anhydrite and limestone additions improved the early strength development. In conclusion, this work demonstrated that it is possible to convert 100% BR to valuable products. However, the production of slags with a GBFS-like chemistry required the use of high quantities of slag-forming agents. Also, the process will be energy intensive and costly. Still, the approach can be economically viable, as several valuable products can be generated. The possible avoidance of landfilling or even to recovery landfill capacities presents another important economic benefit.

Properties of polypropylene fiber reinforced cellular lightweight high calcium fly ash geopolymer mortar

In this study, fly ash (FA) was used as a starting material to develop an environmentally friendly polypropylene fiber (PPF) reinforced cellular lightweight high calcium fly ash geopolymer mortar (PPF-CLFAG). The high calcium FA, a by-product of coal based electrical power plant from Mae Moh, Thailand, was used as the starting material. The PPF contents of 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, and 3% by weight of FA, NaOH at concentrations of 2, 4, 6, and 8 molars, and foam contents (Fc) of 0%, 1%, and 2% of total weight were tested. The unit weight, compressive strength, flexural strength, and scanning electron microscope imaging were tested at the age of 7 days. The dry unit weight was found to decrease with the increasing PPF content and Fc. Whereas, the dry unit weight decreased as NaOH concentrations decreased. The sample with 3%PPF, 2 M NaOH, and 2% Fc had the lowest dry unit weight of 541 kg/m3. The highest compressive strength was obtained with 0.5%PPF content, whereas the highest flexural strength was observed with 2.5%PPF content, regardless of the NaOH concentration and Fc. According to Thailand Industrial Standard (TIS), all mixtures in this study passed the TIS minimum strength requirement for cellular lightweight concrete blocks. The maximum flexural strength of 3.85 MPa and density of 1279 kg/m3 were obtained with the sample with 2.5%PPF and 8 M NaOH with no foam. Empirical equations to predict dry unit weight, compressive strength, and flexural strength of PPF-CLFAG for a given NaOH concentration, PPF content, and Fc were proposed.

Investigation of waste clay brick as partial replacement of geopolymer binders for rigid pavement application

Waste clay brick (WCB) is identified as a feasible alternative cementitious material for producing geopolymer binders to replace ordinary Portland cement (OPC). This study investigated mechanical properties and environmental impacts of one-part geopolymer binders at ambient curing conditions, employing binary blends of WCB with fly ash or slag, while using anhydrous solid sodium metasilicate as the sole activator. WCB was replaced separately with fly ash and slag at 20%, 40%, 60% and 80% by mass to obtain the aluminosilicate precursors. Combination of the aluminosilicate precursors and the solid activator was considered as the total binder. The effect of the alkali activator content, particle size and water-to-binder ratio on compressive strength development were investigated. The strengths of the geopolymers were compared with minimum concrete strength requirements indicated in Australian pavement design guidelines and American Association of State Highway and Transportation Officials (AASHTO) guidelines. The experimental results indicated an optimum activator content of 10% by mass of the total binder for all binary geopolymer systems. Compared to WCB alone and WCB-fly ash blends, binary geopolymer systems of WCB-slag blends showed higher compressive strengths. WCB-slag blends showed high early strength gain and achieved more than 22% and 48% of its corresponding 28-day strength within 24 h and 72 h, respectively. Highest 28-day compressive strength of 81.8 MPa was achieved for the binder with 40% WCB and 60% slag in the precursor. The strength further improved to 96.8 MPa by reducing WCB particle size from 150 µm-passing to 75 µm-passing. Additionally, the environmental impacts associated with the different blends were evaluated considering carbon dioxide emission and energy consumption during their production. These values were subsequently compared with those of OPC manufacturing. The comparison showed that WCB based geopolymer binders can reduce carbon emissions up to 78% and energy consumption up to 85%.

Assessment of Workability and Compressive Strength of Rice Husk Ash-Blended Palm Kernel Shell Concrete

The evaluation of agro-industrial by-products as alternative construction materials is becoming more significant as the demand for environmentally friendly construction materials increases. In this study, the workability and compressive strength of concrete produced by combining Palm Kernel Shell (PKS) and Rice Husk Ash (RHA) was investigated. Concrete mixes using a fixed content of 15% RHA as replacement for cement and 20, 40, 60, 80 and 100% PKS as replacement for crushed granite by volume with the mix ratios of 1:1½:3, 1:2:4 and 1:3:6 were produced. The water-to-cement ratios of 0.5, 0.6 and 0.7 were used for the respective mix ratios. Concrete without PKS and RHA served as control mix. The fresh concrete workability was evaluated through slump test. The concrete hardened properties determined were the density and compressive strength. The results indicated that the workability and density of PKSC were lower than control concrete, and they decreased as the PKS content in each mix ratio was increased. The compressive strength of concrete at 90 days decreased from 27.8-13.1 N/mm2, 23.8-8.9 N/mm2and 20.6-7.6 for 1:1½:3, 1:2:4 and 1:3:6, respectively as the substitution level of PKS increased from 0-100%. However, the compressive strength of concrete increased with curing age and the gain in strength of concrete containing RHA and PKSC were higher than the control at the later age. The concrete containing 15% RHA with up to 40% PKS for 1:1½:3 and 20% PKS for 1:2:4 mix ratios satisfied the minimum strength requirements for structural lightweight aggregate concrete (SLWAC) stipulated by the relevant standards. It can be concluded that the addition of 15% RHA is effective in improving the strength properties of PKSC for eco-friendly SLWAC production..

Experimental Study on Partial Replacement of Materials like Industrial Waste & Rice Husk with Clay Mortar

Abstract: Ancient peoples were used mud mortar for their stone houses. The result was a stone home that was both solid and warm and lasted for lifetimes. Mud made houses creates wonderful warm houses as compared to concrete made houses. In the history of construction, clay mortar was followed by lime mortar. Cement manufacturing is one of the major contributors in global warming and climate change. Also fine aggregate is the natural resource and it is limited in nature, thus industrial sand can be alternative for fine aggregate. We are going to use PPC cement because PPC cement resist sulphate attack more than OPC cement and also it is quite cheap. The setting time of the PPC cement is more than OPC cement but when it settled completely then it gives more strength more than OPC cement. Also they used river sand in there project and nowadays there is shortage of river sand that’s why we are going to use foundry sand partially replacement with sand. Foundry sand is a industrial waste sand so we can save money by using foundry sand. The mortar with the alternative fine aggregate, mixed with different combinations of binding materials. We take White clay to River sand proportion as 1:1. In that we partially replace white clay with PPC cement and in other hand River sand partially replaced with Industrial waste(Foundry sand) and also with Rice husk and that mix proportions was tested for 28 days Compressive strength & after curing of 28 days ,cubes cured in acid & alkali solution for Durability strength. The mortar with 20% PPC cement + 80% white clay & 40% foundry sand + 60% river sand (proportion of white clay to river sand is 1:1) has compressive strength in the range of 4.38MPa (Compressive strength) & 4.42Mpa (Compressive strength after Durability test) and these mixes compared with 1:6 conventional mortar proportion, which is acceptable as per the IS code 2250-1981 specification, the minimum strength requirement of mortar to be 3 MPa. Therefore, the use of stabilized mud mortar in construction would prove to be sustainable as well economical. Keywords: Mud mortar, Foundry sand, PPC cement, Compressive strength, Durability test.

Effect of filler wire strength on high strength low alloy steels

Fusion welding of Ti-Nb microalloyed steels often leads to softening in the heat affected zone (HAZ) due to weld thermal cycles. Apart from heat input and width of HAZ, selection of filler wire also plays an important role, to achieve the minimum strength requirement of the parent material. Steel plates with 800 MPa ultimate tensile strength were butt welded using pulsed gas metal arc welding (P-GMAW) process, with undermatching, matching and overmatching strength filler wires. Welding parameters were selected in such a way that the heat input per unit weld length is almost constant. In all the samples, microstructural features were similar in the HAZ region. Static tensile tests indicated that failure in the samples welded using undermatching filler occurred at welded region, whereas the samples welded with matching and overmatching fillers failed at HAZ region. Further fracture studies indicated that, in case of under matching filler wire samples, crack propagates along the Widmanstatten ferrite present in the weld zone, whereas in other two samples, crack initiated at coarse TiN – matrix interface in the HAZ region. This study shows that overmatching fillers are recommended to overcome strength loss due to HAZ softening.

Seismic Analysis of Multi-Storey Structure Subjected To Different Ground Motions

Major Construction project in urban India is incorporated with Reinforced Concrete (RC) frames, which experience both static and dynamic forces during their lifetime. Static forces can easily be analysed whereas dynamic force analysis is very time consuming, but it can’t be left unanalysed as the results may be catastrophic. Earthquake is an important dynamic force which a building may experience during its lifespan and is therefore its analysis becomes a critical step in design.
 The present work in its utmost sense, aim at understanding the influence of different ground motions on the structure over its life span. This providing new parameters and information to help improve design work.
 INTRODUCTION
 During an earthquake, the structure undergoes dynamic motion due to reaction of the inertia forces built up in the direction against the acceleration of seismic forces. These inertia forces, also known as seismic forces, are considered by assuming pseudo external forces acting on the building. Excluding gravity loads, predominant structure experiences significant lateral forces of considerable magnitude during seismic action. Thus, before the designing of the structure is carried out, it becomes integral to identify and estimate the magnitude of lateral forces acting on the structure.
 Reinforced concrete structures are routinely designed for higher strength parameters than the necessary service load constraints. In general, the members are designated with greater dimensions and higher material standards than the minimum strength requirements specified in the IS design codes. The design procedures for seismic loads also results with greater strength parameters. Furthermore, the redundancy of the structure under the account of division of stresses will also lead to increased overall strength. The current study understands the comparison of storey displacement, base shear, and storey drift of RC framed structure with in individual seismic regions of Indian sub-continent.

The Application of Spent Coffee Grounds and Tea Wastes as Additives in Alkali-Activated Bricks

The traditional firing process to manufacture building bricks is not sustainable because of the high firing temperature and greenhouse gas emission. Therefore, there is a growing incentive to invest in green technologies with minimal environmental impacts. This study ascertained the potential use of Spent Coffee Grounds (SCG) and Tea Waste (TW) as additives to manufacture unfired clay bricks through alkali-activation. The ambition of this study is to divert SCG and TW from landfills and promote sustainable construction practice. An alkali-activated binder was used in this study by activating mill clay residues (precursor) with a liquid mixture of NaOH and Na2SiO3 solutions at a fixed Na2SiO3/NaOH ratio of 0.7. Small amounts (1, 2.5, 5, 10 and 15 wt%) of SCG and TW were added to the binder and mechanically blended for 2.5 min. Block samples were moulded by compressing the slurry in a steel mould. Once demoulded, the block samples were dried in an oven temperature at 110 °C for 24 h, then cured at ambient temperature. Fabricated samples were subjected to unconfined compressive strength test, moisture absorption test and tested samples were also characterised by Optical and Scanning Electron Microscopy (SEM). SEM micrographs showed the discovery of active fungi in the samples containing high SCG content (5 wt% and above) but not in the samples made with TW. The results showed that the samples with up to 2.5 wt% SCG and 10 wt% TW met the minimum compressive strength requirement (8.6 MPa) for structural applications with satisfactory moisture absorption values, as per ASTM C62.

Incorporation of Wheat Straw Ash as Partial Sand Replacement for Production of Eco-Friendly Concrete

The depletion of natural sand resources occurs due to excessive consumption of aggregate for concrete production. Continuous extraction of sand from riverbeds permanently depletes fine aggregate resources. At the same time, a major ecological challenge is the disposal of agricultural waste ash from biomass burning. In this study, an environmental friendly solution is proposed to investigate the incorporation of wheat straw ash (WSA) by replacing 0, 5, 10, 15, and 20% of sand in concrete. Characterization results of WSA revealed that it was well-graded, free from organic impurities, and characterized by perforated and highly porous tubules attributed to its porous morphology. A decrease in fresh concrete density and an increase in slump values were attained by an increase in WSA replacement percentage. An increasing trend in compressive strength, hardened concrete density, and ultrasonic pulse velocity was observed, while a decrease was noticed in the values of water absorption with the increase in WSA replacement percentages and the curing age. The WSA incorporation at all replacement percentages yielded concrete compressive strength values over 21 MPa, which complies with the minimum strength requirement of structural concrete as specified in ACI 318-19. Acid resistance of WSA incorporated concrete improved due to the formation of pozzolanic hydrates as evident in Chappelle activity and thermogravimetric analysis (TGA) results of WSA modified composites. Thus, the incorporation of WSA provides an environmentally friendly solution for its disposal. It helps in conserving natural aggregate resources by providing a suitable alternative to fine aggregate for the construction industry.

Durability of Normal and Lightweight Aggregate Mortars with Different Supplementary Cementitious Materials

A study on the durability parameters of normal and lightweight aggregate mortars, incorporated different supplementary cementitious materials (SCM) is presented. Mortars were prepared using limestone or pumice as aggregates and Metakaolin, Fly ash, Granulated Blast Furnace Slag and Silica Fume, as SCM, that they replaced cement, at 10 % by mass. Ten different mortars, having same water to binder ratio and aggregate to cement volumetric ratio, they were compared mainly in terms of durability. The use of pumice sand was proved to be effective not only to the density of the mortars as it was expected, but also in durability, fulfilling at the same time minimum strength requirements. The addition of the different SCM further enhanced the durability of the mortars, where Metakaolin was found to be the most effective one, especially against chloride’s ingress.

3D printing eco-friendly concrete containing under-utilised and waste solids as aggregates

3D concrete printing is an emerging construction technology, and presents an opportunity for utilising materials that are otherwise considered unsuitable for concrete construction. Incorporating underutilised solids and/or waste solids as aggregates is a way of gaining the maximum environmental and economic benefits from the emerging 3D concrete printing technology. In this study, desert sand (small size), river-sediment ceramsite sand (medium size), and recycled concrete (large size) were experimentally investigated for use as aggregates in the 3D printing of concrete. Three mixtures were designed with continuous, open, and interrupted gradations of solids, respectively, based on the theory of particle interference, and aiming to meet the requirements of extrusion-based 3D printing. The influences of the particle grading characteristics on the printability-related early-age behaviours, mechanical properties, and shrinkage resistance have been measured and analysed. The test results demonstrate that the self-supporting skeletal effect formed by the gradated particles reduces the flowability of the mixtures, but the structural build-up/buildability performance is improved (under the premise of the desired printability). The interlayer distribution and skeleton of the gradated aggregate contribute to improving the interfacial interlocking effect and contact bonding between layers; this is visually validated through computed tomography (CT) scanning. Further, the addition of aggregates reduces the proportion of cementitious composites, and therefore effectively mitigates the shrinkage of the cement matrix. The grading characteristics of the underutilised particle resources are crucial for regulating the early-age 3D printability. This article provides feasible solutions based on experimental data for promoting the eco-utilisation of underutilised and waste solids in 3D printing, and these solutions satisfy the minimum strength and durability requirements.

Lightweight recycled gypsum with residues of expanded polystyrene and cellulose fiber to improve thermal properties of gypsum

In this study, different proportions of gypsum composite reinforced with recycled cellulose fibers and expanded polystyrene were produced to study the properties of thermal conductivity, density, and flexural strength to be used as sealing plates to improve the thermal comfort of buildings. Different gypsum matrix composites were produced with varied proportions of cellulose fiber and expanded polystyrene, to analyze the influence of residues on the properties of the material. The thermal conductivity obtained for composites with greater amounts of expanded polystyrene was 0.18 W/mK, a 48% reduction in relation to plasterboard, improving thermal performance. The flexural strength was also analyzed, which met the minimum strength requirement for use as gypsum composites, however, it is not enough to be used in places that require mechanical resistance, thus it is indicated for sealing plates applications, improving the thermal performance of places where only plasterboard is used.

Compressive stress-strain behavior of concrete with artificial lightweight aggregates and steel-fibers

Artificial lightweight aggregate used in the concrete mix is able to reduce the volume of concrete so that when applied to structural concrete it will reduce the weight of the structure. To be used in the structural concrete mix, the compressive strength produced must be able to meet the minimum requirements of structural concrete compressive strength. The addition of steel fibers to concrete with artificial lightweight aggregate can provide a good behavior change to its mechanical properties. This research was conducted experimentally which investigated compressive stress-strain behavior, the main ingredients used to make artificial lightweight aggregate were Styrofoam and acetone with the composition of 0%-100% of coarse aggregate and to increase the compressive strength of steel fibers by 0%-1.5% from the specimen volume. The specimen used was a 100×200 mm cylinder tested using a Universal Testing Machine, the output obtained was the value of stress and strain. The test results show that the stress-strain of the concrete increases with increasing steel fiber composition. Strain value increased by 23% from normal concrete strain. The compressive strength produced from concrete with a mixture of lightweight artificial aggregates and steel-fibers is able to reach the minimum concrete compressive strength requirements.

Concrete Brick Properties Incorporating EPS and POFA as Replacement Materials

The implementation of sustainable construction and green building becomes the main attention of construction industries in Malaysia as it has been introduced by the government in the Construction Industry Transformation Programme (2016-2020). Therefore, this study focuses on the development of sustainable concrete bricks containing Expanded Polystyrene (EPS) and Palm Oil Fuel Ash (POFA) as sand and cement substitute materials. The percentage of replacement is 20%, 30%, 40% and 50% for EPS and 5%, 10%, 15%, 20% and 25% for POFA. There are 30 different mix designs of brick have been produced and their properties have been identified. Hardened brick density, compressive strength, water absorption and initial rate of absorption are the brick properties identified in this study. Based on the experimental results, it was found that the hardened brick density and compressive strength of the brick decreased as the replacement percentage increased. On the other hand, the water absorption and initial rate of absorption of the brick decreased as the percentage of EPS increased and increased as the percentage of POFA increased. Based on the findings, it shows that EPS and POFA has significantly contributes to the reduction of brick density. Next, for the compressive strength all the bricks have satisfied the minimum strength requirement of non-load bearing brick. Finally, for water absorption and initial rate of absorption, it has been found that majority of the bricks have an acceptable value based on standard requirements for brick. This can be concluded that EPS and POFA could be potential substitute materials for the manufacture of sustainable bricks.

Properties of a New Insulation Material Glass Bubble in Geo-Polymer Concrete.

This paper details analytical research results into a novel geopolymer concrete embedded with glass bubble as its thermal insulating material, fly ash as its precursor material, and a combination of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) as its alkaline activator to form a geopolymer system. The workability, density, compressive strength (per curing days), and water absorption of the sample loaded at 10% glass bubble (loading level determined to satisfy the minimum strength requirement of a load-bearing structure) were 70 mm, 2165 kg/m3, 52.58 MPa (28 days), 54.92 MPa (60 days), and 65.25 MPa (90 days), and 3.73 %, respectively. The thermal conductivity for geopolymer concrete decreased from 1.47 to 1.19 W/mK, while the thermal diffusivity decreased from 1.88 to 1.02 mm2/s due to increased specific heat from 0.96 to 1.73 MJ/m3K. The improved physicomechanical and thermal (insulating) properties resulting from embedding a glass bubble as an insulating material into geopolymer concrete resulted in a viable composite for use in the construction industry.

Sustainable materials in the production of pavement base and subbase courses

The use of sustainable materials in construction is the need of the hour amidst the depletion of natural resources at a rapid rate. The significance of green roads is increasing day by day and green approach for road construction can be only achieved by the use of sustainable construction materials. In the present study, an effort has been made to make base and subbase courses sustainable using Reclaimed Asphalt Pavement (RAP) and Ground Granulated Blast Furnace Slag (GGBS) along with a very less quantity of cement. RAP used in the present study was obtained from the in situ milling of NH-16 at Srikakulam. To meet the gradation requirements as per IRC Ground Granulated Blast Furnace Slag (GGBS) was used along with RAP. Upon initial trial tests, it was concluded that unbound specimens made with RAP and GGBS have failed to meet the minimum unconfined compressive strength(UCS) requirements as per IRC: SP-89:2010 due to which cement by weight of 2% of total mix was added to meet the UCS requirement of 4.5 MPa at seven days. The optimum proportion of RAP that can be used to replace virgin aggregate (VA) was found to be 30% based on UCS test results. The durability studies of GGBS stabilized RAP/VA mixes were found to be satisfactory. The retained strength of the samples after durability studies is 91.43% which is greater than 80% as specified by IRC: SP-89:2010.

Estimating the compressive strength of geopolymer recycled concrete

Abstract Research has shown that different types of waste from industrial and agricultural activities can be used as a partial or complete substitute for traditional concrete materials to save costs and conserve natural resources. This study, therefore, explores the use of geopolymer binders (coal fly ash (CFA) and rice husk ash (RHA)) as a partial substitute for cement (0%, 5%, 5%, and 15% for CFA; and 0%, 5%, 10%, and 20% for RHA, by wt of cement) and cupola furnace slag (CFS) as a coarse aggregate (0%, 5%, 10%, and 30%) of prod. A mixture of 8 M sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) as alkaline activators was used to synthesize geopolymers. Tests such as workability and compressive strength were performed on both fresh and hardened GPRC. The results showed that incorporating 15%CFA, 20%RHA, and 30%CFS increases the workability by 68.57%, but the compressive strength is slightly reduced. It can be concluded that the addition of 5% CFA, 10% RHA, and 10% CFS (i.e., GPRC2) gives an optimum compressive strength of 21.60 N/mm2 and 23.55 N/mm2, respectively, at 28-d and 56-d, compared to a minimum strength requirement of 20 N/mm2.

Recovery of Silicon Dioxide from Waste Foundry Sand and Alkaline Activation of Desilicated Foundry Sand

This study was conducted to recover silica (desilication) as a valuable metalloid from waste foundry sand (WFS) by a leaching process and to find application for desilicated foundry sand (DFS). The leaching time applied was 5 h; 3 M of potassium hydroxide (KOH) was used as a leaching reagent. The agitation speed of 200 rpm and the liquid/solid ratio of 25 were found to be the best conditions for optimum leaching results. A geopolymer from DFS was developed by using NaOH as an alkaline activator. The results obtained showed that the optimum conditions for the synthesis of a geopolymer were 15 M NaOH, 150 µm DFS particle size, and a curing temperature of 80 ℃ for 72 h. The geopolymer strength development was due to the formation of Phillipsite and Kalsilite as new hydration products. At the optimum alkaline solution concentration, the highest unconfined compressive strength (UCS) of 4.8 MPa was achieved. The developed geopolymer met the minimum strength requirements for load bearing material. This study provides an innovative and novel solution for the beneficiation of spent foundry sand and the recovery of a valuable metalloid, resulting to zero waste generation.Graphical