Properties of Fly Ash-Slag-Based Geopolymer Concrete with Low Molarity Sodium Hydroxide

Most geopolymer concrete is produced using low-calcium fly ash and cured at high drying temperatures. Additionally, the activator is prepared with a sodium hydroxide (SH) solution of high molarity. This research proposes using a low molarity SH solution to produce fly ash-slag-based geopolymer concrete cured at room temperature. The properties to be investigated include workability, water absorption, and compressive strength. The influence of mixture composition, i.e., slag content, sodium silicate to sodium hydroxide (SS/SH) ratio, and alkaline activator to binder (Al/Bi) ratio on those properties is of interest. The slag substituted fly ash at 10, 20, 30, 40, and 50% replacement levels. The SS/SH ratio is 1.0, 1.5, and 2.0, with the SH molarity determined at 2M. The Al/Bi ratio is 0.40, 0.45, and 0.50. The results show that a higher percentage of slag reduces slump and water absorption but increases the compressive strength of the geopolymer concrete. The mixtures suitable for use are at the percentages of slag 20, 30, and 40%. An increase in the SS/SH ratio decreases the slump and water absorption. Geopolymer concrete with an SS/SH ratio of 1.5 gives maximum compressive strength compared to the other ratios. Increasing the ratio of Al/Bi increases the workability of geopolymer concrete. At an Al/Bi ratio of 0.45, the compressive strength is maximum and the water absorption is minimum. The recommended mix design in terms of workability, water absorption, and compressive strength of geopolymer concrete is a mixture with slag contents of 20, 30, and 40%, a SS/SH ratio of 1.0 and 1.5, and an Al/Bi ratio of 0.45 and 0.50. Doi: 10.28991/CEJ-2023-09-02-010 Full Text: PD

Flexural Behavior of Steel-Fiber-Added-RC (SFARC) Beams with C30 and C50 Classes of Concrete

Although conventional reinforced concrete (RC) is the most globally used building material; however, its detrimental structural characteristics such as brittle failure mechanism in tension need to be improved. Discrete and short steel fibers (SFs) can be added into the concrete mix to improve its brittleness. The effects of the addition of optimum percentage of SFs on flexural behavior of RC beams have been investigated in this paper. In this study, the optimum percentage of hooked-end SFs with the dimensions of 0.75 mm in diameter and 50 mm in length are added in RC beams with two different classes of concrete (i.e. two different compressive strengths of 30MPa (C30) and 50MPa (C50)). In order to determine the optimum percentage of SFs added to the concrete mix, 15 prisms and 30 cubes with 5 different percentages of SFs (i.e. 0%v/v, 0.5%v/v, 1%v/v, 1.5%v/v, and 2%v/v) from both C30 and C50 classes of concrete have been tested. Based on the results of the flexural strength and compressive strength tests, it is found that the optimum value is 1% by volume (i.e. 78.5 kg/m3) for the specific type of fiber used in this study. Subsequently, to investigate the flexural behavior of steel fiber added RC (SFARC) beams compared to conventional RC beams with no SFs, two RC beams with the dimensions of 170 mm in height, 120 mm in width, and 2400 mm in length, with the SF percentages of 0 and 1%v/v and both having exactly the same steel reinforcement were tested under flexure using a four-point loading test setup for both C30 and C50 classes of concrete. The experimental results show that the SFARC beams with 1% by volume of the SFs have higher first cracking strength, ultimate flexural strength, stiffness, and ductility compared to that of the conventional RC beams with no SFs. Furthermore, the addition of the SFs has more effects on the RC beams with higher compressive strength (50 MPa) compared to lower concrete grade (30 MPa)

Effect on compressive strength of epoxy-modified mortar with further dry-curing

The percentage of concrete porosity will affects the strength and performance of the concrete. It is believed that, with an additional curing, the porosity of the concrete becomes lower and the strength will increase. This paper presents a relationship between the strength development and porosity of epoxy-modified mortar. Epoxy-modified mortar is a type of polymer-modified which uses an epoxy resin without hardener as an addition material. Mortar specimens were prepared with a mass ratio of 1:3 (cement: fine aggregates), water-cement ratio of 0.48 and epoxy content of 5, 10, 15 and 20% of cement. The specimens were subjected to dry and wet-dry curing and the tests conducted were workability, setting time, compressive strength, flexural strength, tensile splitting strength, porosity and strength development. Results show that workability and setting time of the mortar decreased as epoxy content increased. Compressive, flexural and tensile splitting strengths of epoxy-modified mortar with wet-dry curing were significantly higher and became constant at 10% of epoxy resin content. A significant improvement in strength development of mortar without hardener was achieved even after 365 days of curing. The porosity of the mortar decreased as strength development increased. This was due to the gradual hardening reaction of epoxy resin with cement hydrates that filled the void inside; hence produced a denser and stronger mortar

Performance of sawdust concrete at elevated temperature

The aim of this study was to shows the behavior of sawdust concrete at elevated temperature. Sawdust is considered as waste material but nowadays this waste material is utilized in the construction of the building as sawdust concrete. Sawdust is a by-product of wood which is generally used in the production of lightweight concrete, possessing low thermal conductivity. In this study sawdust concrete was made at three different proportions of cement and sawdust 1:1, 1:2, 1:3 by volume. At these proportions, the physical and mechanical properties such as density, workability, strength, fire resistance, mass loss, ultrasonic pulse velocity and residual strength were investigated after 28 days of curing. It was found that with the increment in the amount of sawdust, the workability and strength decreases, however in terms of fire resistance, concrete with lower amount of sawdust performed well. Considering the overall physical and mechanical properties, sawdust concrete can be used in building construction

Effect of recycled homogeneous ceramic waste aggregates on water absorption of mortar

Nowadays, concern for environmental issues encourages the researchers to find a solution for reducing depletion of natural resources. Utilizing the industrial wastes as a construction material is a win-win situation which has two benefits; first, will solve the problem of the landfill and on another hand by recycling and reusing the waste will increase natural materials reservation life span. Ceramic wastes are one of the by-products of ceramic manufacturing, which is directly meant for landfill ends traditionally. There have been several studies on replacement of ceramic waste with concrete admixture. However, there is no research on the effect of the using high rate of ceramic waste replacement on the rate of water absorption. This experimental work focuses on utilizing the homogeneous ceramic wastes as recycled aggregates and partial cement replacement and verifies the effect of this replacement on water absorption of mortar. River sand fully replaced by recycled ceramic aggregates and 40% of cement was replaced by fine ceramic powder. The specimens were cast in 100 x 100 x 100 mm cube for compressive strength test and water absorption test. Mortar containing the recycled ceramic wastes shows lower water absorption in compared to control specimens where the rate value, at the age of 90 days, are 1.32% and 2.11%, respectively

Mechanical and shrinkage properties of hybrid steel and polypropylene fibre reinforced concrete composite

An experimental study had been carried out to investigate the mechanical properties, expansion and shrinkage of fibre reinforced concrete composite (FRC). However, instead of using single type fibre of either steel (SF) or polypropylene (PPF), this study also combined the two types in one mix.The mechanical properties investigated in this study include compressive strength, splitting tensile strength and flexural strength. Three different FRC mix proportions and one normal concrete (control) were casted which includes (a) 75% SF, (b) 75% SF + 25% PPF, (c) 25% PPF, and (d) 0% fibre for control (PC). Meanwhile, the volume fraction, Vf for the FRC was fixed at 1.5% and the concrete strength was designed to achieve grade C60 at 28 days. The results show that the use of fibres in concrete decreased the workability of concrete. In addition, concrete mix with both SF and PPF produced the highest splitting tensile and flexural strengths by an increase of 75.9% and 86.5%, respectively as compared with the control. Furthermore, expansion and shrinkage of FRC was found to be less than the control. It can be concluded that the combined SF and PPF in concrete gives the most appropriate combination as regards to the highest flexural and splitting tensile strengths, and also reduced the shrinkage strain

Strength characteristics of iron ore tailing concrete

Materials used in proportioning of concrete have significant impact on the properties of concrete produced. Iron ore tailings (IOTs) is a waste product generated from the production process of iron ore. In this study, IOTs is used as partial replacement for natural sand in the production of normal strength concrete. Samples of Iron ore tailings from two different mines in Kota Tinggi were collected. The Physical properties of natural sand and these Iron ore tailings were determined. The Energy Dispersive X-ray Spectroscopy (EDS) and the microscopic image of these materials were also studied. Normal strength concrete was designed based on water/cement ratio of 0.54 and cement content of 463Kg/m3 was used in preparing the fresh concrete. For each kind of Iron ore tailings concrete, four different types of concrete samples were produced. The percentage of Iron ore tailings as partial replacement for sand in the sample was varied from 10% to 40% at 10% interval. For each concrete sample, the average of three cubes, three cylinders and three prism specimen results was used for the determination of the compressive strength, splitting tensile strength and the flexural strength respectively. Also studied are the water absorption, the ultrasonic pulse velocity and the mode of failure of the IOTs concrete compared with the normal strength concrete. The concrete sample CZT30 containing 30% IOTs recorded the highest 28days compressive strength of 43.7 N/mm2

Effect of homogeneous ceramic tile waste on properties of mortar

The subject of reduce, reuse and recycle of waste material either from industrial or agricultural sectors is considered very important in the general attempt for sustainable construction. In relation to that, ceramic materials are widely used in many part of the world and consequently, large quantities of wastes are produced simultaneously by brick and tile manufacturers and construction industry. However, part of these wastes and those produced by the construction industry are dumped in landfills. In this present research, the effect of homogeneous ceramic tile waste on harden properties of mortar was investigated. Mortar mixes were prepared focusing on the effect of ceramic aggregates as river sand replacement. Tests were conducted for compressive strength, splitting tensile strength for all mortar specimens. The cement was partially replaced by ceramic powder by 20 %, 40 % and 60 %, respectively by weight of cement. The sand was replaced by ceramic aggregates ranging from 0% to 100% by weight of aggregates. The size of ceramic aggregates used is modified in accordance with ASTM C-33 while the cement was partially replaced by 40 % of ceramic powder by weight of cement. All specimens were cast in 50 mm cubes and cured in water after demoulding until the age of testing. By replacing 100 % of sand with ceramic aggregates, it was found that the compressive strength was very much similar to the control specimen without showing any negative effect. Similarly, by replacing cement with ceramic powder, the strength of mortar shows 10% increment as compared to control specimen. In conclusion, incorporation of homogenous ceramic tile waste either as sand replacement or cement replacement both can enhance the properties of mortar in fresh and hardened states

Long term studies on compressive strength of high volume ultrafine palm oil fuel ash mortar mixes

The long term characteristics of nano palm oil fuel ash in the mortar were investigated. This study covers basic properties like the morphology, porosity, compressive strength and microstructure properties with regards to the variations in the mix design process of mortar. To get a better performance in terms of strength development, the ash used has gone through heat treatment and was ground up to nano size. The mortar mixes were cast in 70x70x70mm cubes for compressive strength test. The incorporation of more than 80% nano size palm oil fuel ash as cement replacement has produced a mortar having a compressive strength more than OPC mortar at a later age. By treating the palm oil fuel ash to nano size, help reduce the cost of expensive admixture for improving the compressive strength of mortar. The results also revealed that the compressive strength of mortar using nano size palm oil fuel ash shows higher value as compared to initial strength at the later age of 1 year by 25%. The porosity of 80% nano palm oil fuel ash mortar reduced 51% as the age of curing increased. The overall results have revealed that the inclusion of high volume nano palm oil fuel ash can produce a mortar mix with high strength, low porosity, good quality and most importantly that is more sustainable

Flexural behaviour of reinforced concrete beams with discrete steel - Polypropylene fibres

This paper discusses the experimental results on the flexural test of concrete containing different proportions of steel fibre (SF) and polypropylene fibre (PPF). The flexural test was carried out under 4-point bending load and followed the relevant standards to FRC. Hooked-end deformed SF fibre with 60 mm length and fibrillated virgin PPF fibre with 19 mm length were used in this study. Meanwhile, the concrete was designed for high strength concrete of C60. The mixture included both single SF and PPF, and also the combination of both fibres; Control beam (PC), beam with 75%SF, beam with 75%SF + 25%PPF and beam with 25%PPF. The total fibre volume fraction (Vf) was fixed at 1.5%. The experimental results show that the percentage proportion of combined SF-PPF at 75-25% had the best performance for its flexural capacity. Mixture with single PPF was also found not effective in delaying the onset of tension cracks and to increase the tensile strength of the concrete. Experimental result also shows beam with 75%SF +25%PPF had their structural stiffness improved the most as compared with the others. For the compressive strength, beam with 75%SF + 25%PPF also revealed comparable performance with the control for high strength composite concrete