Air Curing Research Articles

Properties of strain-hardening cement composites with superabsorbent polymer particles

Strain-hardening cement composites (SHCCs), characterised by strain-hardening and multiple cracking behaviours under direct tension, are generally recognised as ductile and durable construction materials. The effect of the addition of superabsorbent polymer (SAP) particles and curing condition on the mechanical performance and microstructure of binary cement-based SHCC material using ordinary cement and fly ash as the cementitious binder was investigated in this study. Three different SHCCs were designed and mixed; the SHCC mixtures were reinforced with 2% polyvinyl alcohol (PVA) fibres by volume and 1% SAP was added to one SHCC mixture. The mixtures were subjected to compressive, flexural and direct tensile tests. The sealing and healing of cracks after direct tensile tests were also monitored by a microscope. The experimental results showed that the use of fine SAP particles led to an improvement in the mechanical properties of the binary cement-based SHCC material even under air curing. The multiple cracking, ductility and crack sealing were also improved by introducing 1% SAP particles. It is thus concluded that the addition of SAP may be an effective method to improve the sustainability of binary cement-based SHCC materials.

Performance evaluation of masonry grout containing high volume of palm oil industry by-products

The rapid depletion of natural resources has led to the need to develop sustainable practices and material in various applications. One such sustainable practice is to divert the waste generated in the palm oil industry into production of building materials. In this study, palm oil clinker (POC) is used to replace cement and coarse aggregate. The POC chunks are crushed to be used as coarse aggregate and further ground to produce POC powder (POCP) to be used as a binder. The physical properties, chemical composition and scanning electronic microscopic studies were conducted to check the feasibility of substitution of up to 50% POCP as binder and up to 100% POC as coarse aggregate. Density, ultrsonic pulse velocity(UPV), compressive strength for air & water curing, flexural, tensile strength, modulus of elasticity in water cured regimes and structural efficiency were evaluated for the samples. Carbon footprint, cost effieciency and energy savings were also evaluated to understand the contribution of POC to sustainability. The results revealed that the ideal mixture of GPP (30% POCP & 50% POC) masonry grout achieved 79% of compressive strength, a 83% of flexural strength, 85% of tensile strength and about 85.5% of modulus elasticity, as compared to control masonry grout. Carbon emissions of GPP was reduced by 21% and 14.60% cost reduction was established, in addition, appreciable energy savings was notified. The study showed that that utilisation of POC as eco-friendly material in masonry grout is highly recommended based on performance and can provide a route to sustanable practices in the building industry.

Design methodology and mechanical properties of Superabsorbent Polymer (SAP) cement-based materials

Superabsorbent Polymer (SAP) is attracting great concerns in cement-based materials. However, the design of SAP cement-based materials is lack of theoretical basis. This study proposed a design methodology of cement-based materials containing SAP based on the criterion of flowability similarity. The workability and mechanical properties of SAP cement-based materials with W/C of 0.30 and 0.35 were studied. The standard extra water diversion rates under different SAP contents were determined. With the increase of SAP content, the standard extra water diversion rates increased. The influence of curing conditions on the strength growth of SAP cement-based materials was also investigated. Under water curing condition, SAP played a negative effect on the compressive strength of cement mortar and concrete; while SAP enhanced the compressive strength at the later age under air curing condition. Different from the compressive strength, SAP helped enhance the flexural strength of cement mortar under both water curing and air curing conditions. The criterion of optimal effect of internal curing was employed to analyze the mechanical properties of cement mortars with 0.5% SAP.

Effect of Curing Methods on Compressive Strength of Sustainable Self-Consolidated Concrete

Concrete can only achieve the desired compressive strength and durability if cured properly for a prescribed period. For most building codes, concrete structural components and systems are designed for the 28-day compressive strength. Nonetheless, concrete structures are cured typically for only 3 to 7 days. There is an increasing use of curing techniques that involve chemical compounds such as acrylic-based compounds. The emergence of such techniques requires investigation of their effectiveness, compared to traditional curing methods. This article presents the findings of a study to compare the compressive strength of concrete cured using three methods, namely submersion in water, air curing under elevated temperature, and curing with a chemical compound. Compressive strength was determined on standard 150 mm x 150 mm x 150 mm cubes made of sustainable self-consolidated concrete (SCC) in which 90% of ordinary Portland cement content was replaced with combinations of high volume ground granulated blast furnace slag (GGBS), silica fume, and fly ash. A total of 20 mixes were tested, the first set of 10 mixes prepared with water to be binder (w/b) ratio of 0.33 and the second set of 10 mixes prepared with w/b of 0.36. For all mixes, samples cured under air with 45 °C temperature produced the highest 28-day compressive strength compared to other curing methods. Similarly, concrete samples cured using the chemical compound produced higher compressive strength compared to the traditional curing method. The sustainable SCC mix producing the highest compressive strength of 76.22 MPa under air curing was prepared with w/b of 0.33, 72.5% slag replacement ratio, 12.5% silica fume replacement ratio, 10% fly ash while Portland cement represented only 10% of the total binder content.

Investigating Zinc Ketoiminates as a New Class of Precursors for Solution Deposition of ZnO Thin Films.

Zinc oxide (ZnO) has been recognized as one of the most promising metal oxide semiconductor material for processing low-cost thin film transistors (TFTs). Within the scope of this work, we demonstrate a simple, stabilizer free and very efficient chemical solution deposition (CSD) route to grow high quality ZnO layers. The identification of a highly soluble zinc ketoiminate precursor that undergoes hydrolysis under ambient conditions with the facile cleavage of the ligands was the key to develop a simple and straightforward process for ZnO thin films under mild process conditions. Upon heat treatment at moderate temperatures, the precursor decomposes cleanly yielding polycrystalline ZnO thin films, which was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The composition was investigated employing complementary techniques such as X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) which revealed high purity ZnO layers. The functional properties in terms of transparency and optical band gap were determined by ultraviolet-visible (UV-Vis) spectroscopy. The transparent ZnO semiconductor thin films serve as active channel layer of thin film transistors (TFT) which was demonstrated by spin coating of the precursor. Subsequent curing in ambient air, yields a 10 nm film that is sufficient to fabricate working TFTs test structures.

Properties of magnesium potassium phosphate cement pastes exposed to water curing: A comparison study on the influences of fly ash and metakaolin

Under moist condition the magnesium phosphate cement (MPC) exhibits poor water resistance. In this study, the effects of metakaolin (MK) and fly ash (FA) on the properties of magnesium potassium phosphate cement (MKPC) pastes exposed to water curing were investigated. The compressive strengths, water resistance and microstructures of the MKPC pastes containing 30 wt% and 50 wt% of MK or FA as replacements of MKPC under various water curing regimes for up to 180 d were examined. Results showed that the water curing yielded much slower compressive strength development and lower ultimate compressive strengths of all the MKPC pastes during the curing age in comparison to air curing. Incorporation of MK or FA improved the water resistance of MKPC pastes and the MK contributed more considerably than the FA. This may be attributed to the reaction of MK in the MKPC system, which led to the formation of an intermixed phase of struvite-K with Al and Si and/or other amorphous aluminosilicate-bearing phase and thus was beneficial for the microstructure densification, compressive strength increase, and water stability improvement of the reaction products in the MKPC pastes. In comparison, fewer contents of Al and Si were incorporated in the hydration product of MKPC pastes containing FA probably owing to the lower reactivity of FA in the MKPC pastes.

Effect of different curing conditions on compressive strength and durability of kenaf fibre reinforced blended cementitious composites

This paper investigates the effect of normal curing (NC), air curing (AC), and burlap curing (BC) under different curing periods on the mechanical strength and durability of kenaf fibre reinforced blended cementitious composites (KFRBCC) with thermally activated alum sludge ash (AASA). The aim is to determine the most efficient condition and period for curing KFRBCC and to assess the effect of accelerated ageing on strength and durability of KFRBCC after wet/dry cycles. Meanwhile, the microstructure of these mixes is observed via scanning electron microscopy (SEM). The KFRBCC is designed to achieve strength beyond 50 MPa after 28 days (d) of curing by adding 2% treated kenaf fibre (KF) and by replacing Ordinary Portland Cement (OPC) with AASA. The findings suggest that compressive strength and durability of KFRBCC with 40% AASA cured under BC after age of 28 d are enhanced. The addition of treated KF with AASA have helped in limiting the reduction in the compressive strength and durability of the KFRBCC, particularly under prolonged curing period.

Investigation on the fracture behavior of foamed concrete

The fracture behavior of lightweight foamed concrete (LWFC) is significantly influenced by microstructural properties, which are ascribed to the arrangement of air bubbles and pores as well as to the presence of different hydration products. In this contribution, an experimental investigation on the fracture behavior of LWFC is performed. Notched beams made of LWFC were tested in three-point bending to determine the fracture energy based on the load-CMOD (Crack Mouth Opening Displacement) curve. The influence of the dry density is explored considering one density for non-structural purposes (equal to 800 kg/m3) and another density for structural applications (1600 kg/m3). Moreover, two curing conditions are considered (air and water). The load-CMOD curves reveal that for lower dry densities the fracture behavior of LWFC is particularly affected by the curing conditions, with better results achieved in air curing conditions, but this influence decreases with higher dry densities. The improved performance in air curing conditions for lower dry densities is also observed in terms of flexural strength, but is not particularly evident for the compressive strength. Micrographs across the crack surface determined via Scanning Electron Microscopy (SEM) are finally presented to analyze the experimental findings and justify the results in terms of microstructural configuration of the specimens.

The influences of cement type and curing condition on properties of pervious concrete made with electric arc furnace slag as aggregates

Pervious concrete is an environment-friendly material in many aspects such as flood control, reducing heat island effect, water purification, providing better anti-skid performance in rainy days and better sound absorption capability. In this article, the influences of cement types and curing condition on properties of pervious concrete made with electric arc furnace slag as aggregates were investigated. Four types of cements (type I cement, type II cement, sulphoaluminate cement and calcium aluminate cement) were used and two curing conditions (saturated lime water curing and air curing) were considered. Results revealed that alumina,ferric oxide, tri-sulfate (AFt or ettringite) formed in pervious concrete made with sulphoaluminate cement, resulted in a serious degradation in compressive strength as well as flexural strength, especially for specimens cured in saturated lime water curing condition. Pervious concretes from type II cement showed better compressive strength and worst permeability while the one from sulphoaluminate cement shows opposite. Air Curing results were lower than lime water curing except concretes from sulphoaluminate cement.

Effects of curing regimes on the physico-mechanical properties of self-compacting concrete made with ternary sands

This paper investigates the effects of curing regimes on the physico-mechanical properties of self-compacting concrete (SCC) made with ternary sands in order to valorize local materials, reuse of industrial wastes and to benefit from their properties for the composition of SCC. Three types of sands were used in ternary combinations: river sand (RS), crushed sand (CS) and dune sand (DS). First, we started by the measurement of the porosity of seven ternary combinations of sand (RS-CS-DS), included the 100%RS as reference combination. Subsequently, the rheological characteristics of SCCs in fresh state are characterized and analyzed. Finally, studying the effects of curing regimes (three regimes were used: wrapped in a plastic sheet, water curing and air curing) on the compressive strength of SCC made with different systems of ternary sands. The obtained results proved that beyond 40% of RS substitution by (CS + DS); the porosity of the sand mixture is increased. The porosity of the combination C2 (60% RS + 20% CS + 20% DS) is lower than those of the other combinations. In addition, the rheological properties of SCC are decreased, which requires the additional quantities of water or superplasticizer to meet the self-compacting properties. Whatever the curing regimes, we can say that the partial replacement of RS by (20% CS + 20% DS) offers the best compressive strength at all ages and gives good rheological characteristics to the SCC. The use of ternary sand (C2) also contributes to the improvement of SCC compactness. The results show that the water curing as well as wrapped curing provide better results than air curing.

MECHANICAL, THERMAL AND DURABLE PERFORMANCE OF WASTES SAWDUST AS COARSE AGGREGATE REPLACEMENT IN CONVENTIONAL CONCRETE

Wood yields a number of by-products and Sawdust is as useful as others. Sawdust is regarded as a waste material and is effectively utilised as sawdust concrete in the construction of buildings. It is capable to be utilised as light-weight concrete and holds the quality of long duration heat transfer. In this study, three different ratios (1:1, 1:2 and 1:3) volume mix proportions of cement to sawdust were adopted to make sawdust concrete. At varied intervals of 7, 28 and 56 days of air curing, thermal and mechanical properties like workability, density, elastic modulus, strength and heat transfer were probed of mentioned sawdust concrete proportions. The resistance to elevated temperatures was also evaluated after 28 days of age; weight loss, residual compressive strength, surface texture and ultrasonic pulse velocity were considered in evaluation process. The findings showed that increase in sawdust volume affected to decrease the workability, strength and elevated temperatures resistance. However, the concrete having higher proportion of sawdust performed competently and well in terms of thermal conductivity. Moreover, a decrease in the heat transfer of sawdust was also observed. Examining the all-embracing mechanical and physical properties, sawdust can be effectively utilised in the construction of buildings.

Self-healing properties of reactive powder concrete with nanofillers

The study presented in this paper aims to investigate the self-healing properties of reactive powder concrete (RPC) modified with nanofillers, which has the self-healing ability of compressive and flexural strength. The inner damage of RPC with nanofillers during loading is analyzed by using an acoustic emission system. Three types of nanofillers (nano-SiO2, nano-TiO2 and nano-ZrO2) and two curing methods (water curing and air curing) are selected for identifying the influencing factors. Experimental results indicate that all incorporated nanofillers have the ability to enhance the self-healing ability of RPC. However, we noted that the enhancement is more evident when the RPC is cured in water. Composite with nano-SiO2 has the largest self-healing coefficients of compressive (Cs) and flexural strength (Fs) with water curing of 1.31 and 1.19, which increases by 39.4% and 33.7% compared to RPC without nanofillers, respectively. The incorporation of nanofillers weakens and even eliminates the Kaiser effect of RPC under secondary loadings, indicating that to a certain extent, crack healing has taken place. The effect of the nanofiller modification mechanisms on the RPC self-healing properties is thought to be attributed to three main features: (1) the provision of nanofillers provides the hydration environment for unhydrated cement particles and nucleation sites for the hydration products; (2) nanofillers improve the 3D network structure of concrete matrix, produce more fine cracks and disperse the propagation direction of the cracks; (3) the pozzolanic reaction of nanofillers (including nano-SiO2 and nano-TiO2), especially for nano-SiO2, produces additional calcium silicate hydration, and increases the compactness of RPC.

Compressive Strength and Water Absorption Behavior of Self-Curing Fiber Reinforced Concrete

Self-curing (internal curing) of concrete using shrinkage reducing admixture, super-absorbent polymers, and pre-saturated lightweight aggregates are established methods to prevent autogenous shrinkage and self-desiccation. However, using polypropylene fiber addition (PPF), that provides better control of plastic settlement and plastic shrinkage cracking are not found in the literature. This research is carried out to compare concrete with the addition of chemical shrinkage reducing admixture named polyethylene-glycol (PEG 400) with and without polypropylene fibers (PPF). The self-curing fiber reinforced concrete of 30 MPa strength, made of 1.5% PEG400 by weight of cement, and with or without 0.5% PPF by volume of fractions were prepared. The mixes were either exposed to air curing in room temperature or in a controlled temperature of 32°C. The compressive strength and water absorption behaviors are monitored. It was found that the use of PEG400 improved the workability but not the strength, while the addition of PPF has less effect on workability but reduces the strength. These results give better understanding PEG and PPF concrete to the industry.

Influence of palm oil clinker powder on the fresh and mechanical properties of masonry mortars

Masonry and rendering mortars are is well known oldest techniques in the building. A common idea is to use strong material as possible, and as a result mortars are often rich in cement. Not only this is unnecessary expensive, it has also technical disadvantages and harmful to environment. Hence, in this study focuses on utilisation of palm oil mills waste, namely palm oil clinker powder (POCP) and POCP influences on the fresh and mechanical properties of masonry mortars are analysed and comparison between cement – lime (CLM) and masonry cement mortar (MCM) are addressed. The masonry mortars were prepared using cement – lime and masonry cement as control masonry mortars christened as type ‘S’ mortar. The POCP used as cement replacement material in the masonry mortar mixture from 0-80% by volume in the preliminary study and ideal replacement of 40% was used in the final mixture of mortar for comparison. All specimens were cured in water and air curing regimes for 7, 28 and 56 days and the physical and mechanical properties were analysed. The results show that as replacement of cement with POCP increases, there is a reduction in fresh density with subsequent increase in air content. Further, the use of masonry cement with POCP (MCP) shows highly workable mix even at lower w/cm ratio compared to cement-lime mortar with POCP (CLP). Moreover, CLM, CLP obtained higher strength (28 & 20 MPa) than MCM and MCP (24 MPa & 11 MPa). on the contrary, the cement-lime mortar with POCP shows higher compressive strength compared to masonry mortar prepared with masonry cement-POCP.

Properties of sand cement brick containing ground palm oil fuel ash as fine aggregate replacement

The prosperous palm oil industry continues to generate increasing amount of palm oil fuel ash which disposed as environmental polluting waste. Thus, research was conducted to investigate the effect of ground palm oil fuel ash as partial fine aggregate replacement towards properties of sand cement brick. Series of mixes were prepared with 0%, 5%, 10%, 15%, 20% and 25% ground palm oil fuel ash partially substituting the river sand. Two types of curing methods were applied namely water and air curing. The bricks were subjected to compressive strength, flexural strength and water absorption test at 28 days. The results show that utilization of 15% ground palm oil fuel ash as fine aggregate replacement increases the brick strength. The pozzolanic reaction and filler effect of the finely ground ash makes the concrete internal structure denser resulting in strength enhancement. The use of ground palm oil fuel ash in brick production would reduce amount of palm oil waste disposed, save the use of land for dumping purpose and decrease quantity of river sand mined.

Strength deterioration of nano-silica contained in ordinary Portland cement concretes in aggressive sulfate environments

This investigation presents the effect of durability of concrete in aggressive conditions and loss of compressive strength measurements for concrete incorporating 0%, 5% and 10% powdered nano-silica (NS). The important factor in this investigation is air curing, water curing, the kind of the sulfate exposure regions (continuous and drying-immersion cyclic exposures). For this investigation, w/cm (water to cementitious materials) proportion is 0.4, and 0.5. Up to 365 days the decrease in the compressive strength of concrete was examined for the aggressive sulfate conditions. In these concrete specimens, three groups were kept up. In the control assessment of compressive strength reduction, tap water was used, and this was kept up as the first group. Under continuous and cyclic exposures, 10% Na2SO4 was used as a part of alternate groups and the preparation submerged up to 365 days’ time duration. All the blends subjected to the compressive test, and durability studies, such as sorptivity, water absorption, and chloride penetration test. The outcome demonstrates the protection of cement against sulfate attack expanded by incorporating NS types of cement. The advantage of incorporating 5%, 10% NS to the densifier cement concrete, expands strength and reduces permeability.

지황 종근의 저장성 및 수량에 미치는 음건 처리의 효과

지황 종근의 저장성 및 수량에 미치는 음건 처리의 효과

Effect of high MgO content on the performance of alkali-activated fine slag under water and air curing conditions

The present study investigates the effect of magnesium oxide (MgO) on the respective performance of water- and air-cured alkali-activated fine slag (AAS). Ground granulated blast furnace slag (GGBFS) of two different fineness levels were used to produce two AAS mixtures. These mixtures were alkali-activated with sodium hydroxide and sodium silicate and prepared into samples by adding, respectively, 2.5%, 5%, 7.5%, 10% and 15% MgO by total binder weight. A series of tests, including slump flow, setting time, compressive strength, X-ray diffraction (XRD), scanning electronic microscopy (SEM) and thermogravimetric analysis were conducted in accordance with the relevant standards. In terms of findings, the addition of MgO promoted the hydration of AAS significantly at early curing ages. Optimum MgO content was 7.5% for slag-4000 specimens and 5% for slag-6000 specimens. Cracks were observed in the water-cured AAS samples, with greater cracking at higher levels of MgO content. Moreover, the results show that the main contribution of MgO is in the hydrotalcite-like phase (Ht), where it adds volume, which improves strength the AAS paste. The effect of MgO was significantly increased in the samples that used finer-particle GGBFS. Adding MgO contributed to the more formation of hydration products, which was observed in the present study using X-ray diffraction and SEM and derivative thermogravimetric analysis.

PROPERTIES OF MORTAR REINFORCED WITH NATURAL HORSE HAIR AND KENAF FIBRES

Cement based materials such as concrete and mortar are widely used in construction industry. One of the drawbacks of concrete or mortar is its low tensile strength that will affect cracking. Thus, enhancing its tensile strength using short fibres is beneficial in reducing problems caused by cracks. This study highlights the effects of natural horse hair and kenaf fibres with different curing conditions on the properties of mortar. Three different curing conditions were employed namely, water curing, air curing and 7-days in water and thereafter dry curing. The mortar samples, cubes and prisms, were tested in compression and flexure at the ages of 3, 7 and 28 days. In addition, the water absorption, fibre surface and mode of failure of the samples were also recorded and analysed. The experimental results show that the inclusion of horse hair and kenaf fibres enhanced the flexural strength but reducing the workability of the mortar. The horse hair mortar recorded higher flexural and compressive strengths compared to kenaf fibre mortar. However, the effect of fibres on the compressive strength was not significant in which the control sample recorded higher compressive strength compared to horse hair and kenaf fibre mortars. In addition, the water absorption for kenaf fibre was higher than horse hair due to its porous microstructure. It was recorded also that the samples with natural horse hair and kenaf fibres failed in a ductile manner compared to control sample due to the bridging effect of the fibres that able to hold the matrix together.

The Effect of Using Lightweight Aggregate on Some Properties of Cement Mortar

The aim of this research is to produce lightweight cement mortar with properties better than reference ordinary cement mortar. Porcelanite stone were utilized as lightweight aggregate with a volumetric partial substitution of fine aggregate. The process includes using different percentages (5, 10, 15 and 20 %) of pre-wetted (24hr.) porcelanite to produce lightweight mortar with internal curing. Water curing was used for reference mortar mixture and air curing for the other mixtures of porcelanite substitution. Compressive strength, flexural strength, density and ultrasonic pulse velocity for different ages (7, 14 and 28 days) have been tested. The results show an improvement in the properties of cement mortar especially in replacement percentage of 10 %.