Concrete Curing Research Articles

Effect of type and particle size of superabsorbent polymers on the hydration mechanism of pavement concrete

ABSTRACT Superabsorbent polymer (SAP) has been accepted as a novel internal curing component in pavement concrete because of its superior water absorption and retention capabilities. The effect of the characteristics of SAP on the hydration of pavement concrete and the understanding of the internal curing mechanism are crucial. In this paper, modified cement-based materials were prepared by incorporating non-ionic and ionic SAPs (SAP-AM and SAP-SA) with different size distributions. The influences of SAP type and particle size on the hydration kinetics, strength and internal relative humidity of pavement concrete were investigated. The results show that SAP-AM and SAP-SA improved the mechanical strength of specimens at 28 d by about 9.7% and 0.3%, respectively. SAP-AM lengthened the acceleration duration, and the delay effect of SAP-AM with the particle size of 80–100 mesh was greater. SAP-AM200 decreased the conversion rate of capillary water to chemical bonding water, thereby reducing the hydration reaction at 1 d. Non-ionic SAP with a smaller particle size is an ideal internal agent for the effective curing of pavement concrete. These new findings may help to understand the hydration mechanism and provide suggestions for the selection of SAP type and particle size in internally cured concrete.

Alkali Activated Fly Ash-Based Concrete: Evaluation of Curing Process Using Non-Linear Ultrasonic Approach

Abstract This paper investigates the applicability of the nondestructive testing and evaluation (NDT&E) method using ultrasonic signals to monitor the curing of alkali-activated fly ash-based concrete (AAFC). The evaluation was carried out on AAFC specimens with two different water/binder (W/B) ratios of 0.3 and 0.5 and after curing at 60 °C for 7, 14, and 28 days, respectively. The signals are recorded and analyzed using linear and non-linear ultrasonic techniques. The results show that the non-linear ultrasonic technique has a clear advantage over the linear ultrasonic technique when monitoring the curing of AAFC specimens with a lower W/B ratio. However, the specimens with the higher W/B ratio do not undergo proper curing and therefore do not show clear distinctions between the curing times measured from the two ultrasonic techniques. The unconfined compressive strength (UCS) of the AAFC specimens at different W/B ratios and curing times is also measured. The UCS results showed a good correlation with the ultrasonic results.

An experimental investigation on compressive strength of concrete with rice husk and cow dunk ash using various curing methods

The method of Curing which encompasses water content humidity and Climatic conditions bears an authority for attainment of Concrete strength. In view of this curing of Concrete consumes huge amount of fresh potable water, which is reported to be in scarcity at different site locations. Furthermore, depletion of ground water table effects the curing for concrete components, warranting for other types of curing methods. Concrete and its production is reported worldwide that is not at all environment friendly owing to its consumption of huge amount of natural resources, water at the same time emitting abundant of unwanted gases to the environment. Thus, in order to tackle with environmental hazards, a need is felt to make use of industrial by products as partially replacement of cement and aggregates in a meaningful waste utilization. In the present work, it is attempted that Cement can be replaced by Fly ash, GGBS, CDA etc., as they have good Confining properties. From the past studies it is observed that cow dung ash is mixed with concrete for generation of light weight concrete. Further this mix was reinforced with addition of rice husk ash as it is rich in silica contents that enhances the concretes additional strength. In the present Case M20 grade concrete has been considered with a variation of CDA 10% and RHA 20%. Subsequently cubes were cast in the laboratory and tested following the standard procedure, subjected to 1% (Polyethylene Glycol 200) was used on the surface in order to get the specimen cured. Experiments conducted yielded a high strength depicting “Spray” as a method of curing, for the conventional concrete. Whereas Ponding method of curing attained a high strength when the cement was replaced by 10% CDA and 20% RHA and 1% Polyethylene Glycol 200 was applied on the surface for curing.

Effect of Curing Methods on the Compressive Strengths of Palm Kernel Shell Concrete

Appropriate curing of concrete is necessary to obtain maximum durability and achieve designed strength for concrete exposed to different environmental conditions. Curing is regarded as the means of regulating the degree and extent of loss of moisture from concrete when the cement in the concrete is undergoing hydration. This study made a comparative study of the consequence of adopting different methods of curing on the compressive strength of concrete modified with Palm Kernel Shell (PKS) aggregate. Concrete cube specimens of mix ratio 1:1:2 were cast with water-cement ratio of 0.55. The specimens were cured using four (4) different procedures: immersion, sprinkling, wet-curing and open-air. The concrete samples were tested for their compressive strengths at ages 7, 14, 21 and 28 days of curing. The results obtained show that immersion method of curing has the highest compressive strength at 28 days with a value of 17.07 N/mm². This was followed by the sprinkling method of curing with 15.78 N/mm². Wet-curing method has a compressive strength of 14.48 N/mm² and open-air curing has compressive strength of 13.11 N/mm². It was concluded that immersion and sprinkling methods are suitable methods for curing PKS concrete.

GGBS Use in Concrete as Cement Constituent: Strength Development and Sustainability Effects – Part 1

This study, third in the series, following from ground limestone and Class F fly ash, evaluates, as a cement constituent, the effect of using ground granulated blast furnace slag (GGBS) on the strength development of concrete, and consequently its embodied carbon dioxide (CO2e). The paper has been built from systematically analysing, evaluating and modelling the extensive data-matrix developed, having 85,099 data points, from the information sourced from 663 studies published in English, during 1974 to 2020, by 1,672 authors, working in 718 institutions in 49 countries, globally. It is shown that, at a given water/cement ratio, in comparison to Portland cement (PC), the use of GGBS results in a reduction in 28-day concrete strength, which increases with GGBS content, at a rate determined by the strength of concrete, GGBS fineness, and curing of concrete. It is also shown that, as to achieve a 28-day design strength, a lower water/cement ratio is required with a PC/GGBS blended cement than PC, this will reduce the actual CO2e savings that can be realised with the use of GGBS as cement constituent in manufacturing concrete. Finally, it is shown that GGBS is more effective in lowering CO2e of concrete than FA and GLS.

Behaviour of ambient cured prestressed and non-prestressed geopolymer concrete beams

One of the sustainable alternatives to Portland cement is geopolymer concrete consisting of industrial waste. Practical application of geopolymer concrete is restricted as it requires the use of high temperature to develop compressive strength. This study aims to develop a mixture design for geopolymer prestressed concrete specifically designed to take prestressing force using ambient curing technique and compare its performance with the same grade of Portland cement concrete mix. As ambient curing technique is used for geopolymer concrete hence a combination of blast furnace slag and fly ash is taken as source materials and due to ease of availability and economy, sodium hydroxide and silicate are chosen as activators. After several trial mixtures, M 40 grade of geopolymer concrete is developed using an equal proportion of fly ash and ground granulated blast furnace slag (GGBFS) as source material. GGBFS provides early strength at ambient curing in geopolymer concrete and hence was incorporated with fly ash. 3 ply of 3 mm diameter bars were used as pre-tensioning wire. Load v/s deflection graph for non-prestressed geopolymer concrete beams and beams with same grade Portland cement concrete show that the load-carrying capacity of both beams was at par. It was also observed that prestressed geopolymer concrete beams which were cured under ambient curing developed sufficient strength and were equally capable of carrying the load as compared to Portland cement concrete beams. Load carrying capacity increased in prestressed Portland cement concrete beams increased by 78% while in prestressed geopolymer concrete beams the increase was 83% and also the deflection of both prestressed beams was more compared to non-prestressed beams. This indicates that sustainable material can be effectively utilized in prestressing work without comprising on strength.

Research on Curing Water Demand of Cementing Material System Based on Hydration Characteristics.

The performance of cover concrete is acknowledged as a major factor governing the degradation of concrete structures. Curing plays a vital role in the development of concrete durability. The effects of different water-binder ratios and mineral admixtures on the curing water demand of concrete were studied by the surface water absorption test. Combined with the characteristics of the hydration heat and chemically bound water of the composition cementing material system, the law of variation for curing water demand was analyzed. The results show that the addition of mineral admixtures can reduce the early hydration rate and hydration exothermic characteristics, and the hydration degree decreases with the increase of mineral admixtures. Due to the filling effect and active effect, the addition of fly ash (FA) and ground granulated blast slag (GGBS) reduces the curing water demand. The curing water demand of cover concrete decreases with the increase of mineral admixture content, and the curing water demand of pure water is the maximum and that of mix FA and GGBS is the minimum. Moreover, there is a strong correlation between the cumulative curing water demand and the chemically bound water content, indicating that the power of water migration mainly comes from the hydration activity of the cementing material system. The results provide a theoretical basis for the fine control of a concrete curing system.

Mechanical performance and durability of geopolymer lightweight rubber concrete

This research focuses on producing and testing a type of geopolymer concrete as an alternative to the conventional Portland cement concrete. The proposed concrete incorporates lightweight expanded clay aggregate (LECA) and rubber from car tyre waste which results in the production of a new concrete: “geopolymer LECA-Rubcrete”. A total of ten geopolymer concrete mixes were produced using rubber and LECA as partial replacements of fine and coarse aggregates, respectively. Variables such as the ratio of geopolymer binders, LECA pre-treatment, concrete curing method, and mixing procedures were examined. Physical, mechanical, and durability tests were conducted including workability, compressive strength, drying shrinkage, water absorption, surface abrasion, and carbonation. This research aimed to provide the necessary information needed to develop lightweight geopolymer Rubcrete structures to reduce carbon emissions and move a step closer towards a greener future. The results indicated that lightweight geopolymer Rubcrete is a suitable alternative to lightweight conventional concrete with similar or better durability properties. The workability increased by 9% and 20% when using rubber and LECA, respectively; however, the compressive strength decreased by 32% and 67%, respectively. Using 25% slag to 75% fly-ash decreased the workability by 44% and increased the strength by 47%. Specimens cured in the ambient condition showed less strength compared to those cured in water. Heat + water curing showed less strength in all mixes, except in mixes with no lightweight materials and with high fly-ash content, which showed 16–21% strength increase. Of the tested mixes, geopolymer LECA-Rubcrete mix that has high slag content showed comparable or better performance than that showed by Portland cement LECA-Rubcrete mix in all measured characteristics.

Embedded dual PZT-based monitoring for curing of concrete

Monitoring the hardening of concrete during construction, is important to ensure proper strength gain and timely removal of formwork without compromising safety. Existing non-destructive testing (NDT) techniques mostly require sophisticated equipment and technical expertise, which makes it less applicable for field monitoring. Alternatively, lead zirconate titanate (PZT)-based electromechanical impedance (EMI) technique is under research, as an option for monitoring the hydration of concrete. The current study proposes a transducer design using an innovative configuration of PZT patches on metal plate, which enables segregation of flexural and axial modes while measuring EMI. The resultant peaks are more prominent, making its variation easier to track. The effectiveness of this configuration is studied by embedding the smart piezoelectric-based plate in the concrete during casting and recording the electromechanical admittance throughout the curing period. The frequency shift of the first flexural/axial peak, is a good indicator of the strength gain during this period. This has been verified for ordinary Portland cement (OPC) and fly ash-based geopolymer (GP). The results show that the frequency shift curve follows the isothermal calorimetry curves beyond the main hydration peak.

Use of Thermostone Waste Aggregates for Internal Curing of Reactive Powder Concrete

The concrete need curing for cement hydration that is a chemical reaction in each step require water supply throughout the time period. The traditional concrete cured by external method that prevents the concrete surface dry so that keeping the concrete mixture wet and warm. The internal curing was adopted in normal and high strength concrete such as reactive powder concrete. In present paper, experimental approach is to study the mechanical properties of reactive powder concrete cured internally with thermostone material. The materials that adopted to evaluate and find out the influences of the internal curing on the mechanical properties of reactive powder concrete is focused with different curing methods such as in water, air and combined water and air. Thermostone aggregate are used as partial sand replacement by volume with different percentages to explore the percentage that effects of the concrete mechanical properties. Test results showed that the best partial replacement by thermostone is 5% gave enhancement and increase in compressive strength and flexural resistance strength (modulus of rupture) and concrete density. Highest increasing of compressive strength is 10.07in case of 5% partial replacement at 90 days. In case of cured the specimens up to 90 days, the increase in modulus of rupture is 4.53%

The Effect of Curing Methods on Compressive Strength of Concrete

Concrete curing is an effort made to optimize the results of concrete casting. This action needs to be done because it has a major effect on the quality and strength of the concrete, one of which is so that the concrete does not lose moisture too quickly, because later this condition will lead to excessive shrinkage in the concrete. As a result, the concrete can experience cracks. This will cause the construction work to be less qualified and endanger construction users. The purpose of this study is to determine the effect of concrete treatment methods on the value of normal concrete compressive strength. Concrete curing can be carried out by several methods according to the type and condition of the structural elements to be treated. From the results of the study, it was found that the curing method of concrete had an effect on the value of normal concrete compressive strength, namely that the average compressive strength value in the fresh water immersion treatment method was 23.730 MPa, the treatment method for wrapping concrete with gunny sacks was 22.349 MPa, the treatment method of wrapping concrete with plastic is 22.306 MPa, and in the treatment method of pouring concrete with fresh water is 21.199 MPa. The average value of the maximum compressive strength occurred in the treatment method with fresh water immersion, namely 23.73 MPa, and the minimum compressive strength value that occurred was found in the treatment method with fresh water sprinkling, namely 21.199 MPa. Thus, that concrete curing is good, namely, by soaking the concrete with fresh water.

콘크리트 양생용 거푸집의 온도분포 최적화를 위한 유도가열 코일 배열 및 배치 비교평가

This paper proposes coil design conditions of a concrete curing system based on induction heating method for efficient concrete curing. The concrete curing method using an induction heating coil has the advantage of low energy consumption by using a high-efficiency system compared to the existing methods that undergoes several stages of energy conversion. When the induction heating coil is used, it is important to obtain uniform temperature surface on the formwork temperature. When a temperature difference occurs in the vertical section of a concrete form due to an uneven temperature distribution during concrete curing, it may cause a decrease in concrete strength. In this paper, in order to efficiently heat the concrete formwork surface, the temperature distribution according to the arrangement of the induction heating coil was analyzed and the current strength flowing through the coil was studied. The design conditions and results of the induction heating coil were presented using FEM simulation to obtain a uniform temperature distribution. Based on the proposed two-turn induction coil, the temperature distribution inside the formwork was analyzed using the distance between the formwork and the coil and the distance between the coil turns as design parameters. In addition, the simulation results were verified through an induction heating experiment using an experimental formwork.

Investigation of Mechanical and Durability Properties of Concrete Mixed with Water Exposed to a Magnetic Field

Water is a crucial element in the concrete mix and is alone responsible for concrete work ability and cement hydration. The massive quantity of potable water consumed during the production of concrete is a concern. In general, fresh and hard concrete qualities are most influenced by the quantity and water quality. The use of magnetic water in concrete gives many benefits when it comes to increasing its properties. A substantial quantity of water can be saved by substituting potable water with magnetized water in concrete. In this study, the effects of magnetized water on the concrete's mechanical and durability properties were tested. Four different combinations were made using potable water and magnetic water. Mechanical properties including compression, flexural, tensile strength, and SEM analysis were evaluated. Water absorption, acid resistance, and corrosion resistance were all tested as part of the durability tests. According to the results of the experiments, employing magnetic water for concrete preparation and curing enhanced the mechanical properties and durability. Concrete mix MMMC prepared and subjected to curing using magnetized water has a 14.86% greater compressive strength than ordinary concrete. Similarly, tensile and flexural strength of mix MMMC amplified to 14.32% and 14.02%, respectively. Besides, the consumption of chemical admixtures also considerably reduced in magnetized water imbibed concrete.

Correlation Analysis of Heat Curing and Compressive Strength of Carbon Nanotube–Cement Mortar Composites at Sub-Zero Temperatures

Concrete curing under sub-zero temperatures causes various problems, such as initial cracking and a decrease in mechanical strength. This study investigated the effect of sub-zero ambient temperature and multi-walled carbon nanotube (MWCNT) content on the heat and strength characteristics of heat-cured MWCNT cementitious composites. The experimental parameters were the application of heat curing, MWCNT content, use of an insulation box to achieve a closed system, and ambient temperature. The results showed that the internal temperature change of the MWCNT cementitious composite increased with the ambient temperature and MWCNT content. When an insulation box was installed, the maximum temperature change of the MWCNT cementitious composite during curing increased. Furthermore, heat curing increased the compressive strength of the cementitious composite. Moreover, a microstructure analysis using field-emission scanning electron microscopy verified the formation of a MWCNT network among the cement hydrates.

Effects of cement types and addition of quartz and limestone on the normal and carbonation curing of cement paste

Belite-rich cement (BRC) and carbonation curing are vital in the cement and construction industries for reducing carbon emissions and achieving carbon neutrality. In this study, the effects of quartz, limestone, and the type of cement (BRC and ordinary Portland cement) on the carbonation curing and normal curing of cement paste were systematically studied. The water/binder ratio was 0.5, and the replacement ratio of quartz/limestone was 20%. The experimental results showed that adding 20% quartz/limestone to BRC effectively accelerated the carbonation curing process, and the acceleration effect of quartz was more obvious than that of limestone. The compressive strength of the samples with 20% quartz and limestone added to BRC was 72 MPa and 69 MPa, respectively, after 28 days of carbonation curing. These are respectively 1.7 times and 1.6 times higher than the compressive strength of the samples under normal curing. The late-age strength mainly depended on the amount of cement and marginally depended on the addition of quartz/limestone. Quartz improved carbonation efficiency by increasing the porosity of the cement paste and providing nucleation sites for the silica gel formed during carbonation. Moreover, CH, ettringite, monocarboaluminate, and hemicarboaluminate were fully carbonated, and large amounts of alite and belite were carbonated during carbonation curing. The electrical resistivity after 28 days of carbonation curing was 38–72 times higher than its electrical resistivity after 28 days of normal curing. After carbonation curing, the quartz-blended BRC had a high resistivity of 1562 kΩ·cm. Thus, quartz is an effective supplementary material for the carbonation curing of concrete. Moreover, the combination of quartz and BRC has a greater impact on carbonation curing than the combination of limestone and BRC.

Complex Maturity Method for Estimating the Concrete Strength Based on Curing Temperature, Ambient Temperature and Relative Humidity

The maturity method is deservedly considered one of the reliable indirect methods for determining the strength at the early stages of concrete curing. The main parameter in the calculation is the internal temperature of concrete that accumulates during the chemical reaction of concrete curing, while external factors such as ambient temperature and relative humidity are fallaciously omitted. In this work, the complex maturity method was developed based on ASTM C1074, accounting for the influence of ambient temperature and relative humidity and coefficients indicating their influence weight. The laboratory testing to measure the concrete strength by compression method and non-destructive sclerometer method were performed on concrete samples according to ASTM C109, GOST 22690, and GOST 10180. According to the calibration dependence of the existing and proposed methods results in comparison with the strength of cubic samples, the highest coefficient of determination R2 = 0.976 was revealed for the complex method of maturity, which indicates its reliability in contrast with sclerometer and traditional maturity methods. The determination of complex maturity allows for an evaluation of the current state of concrete strength, but also reduces the waiting time for concrete curing and increases the economic effect during construction.

Experimental investigation on bond behaviours of deformed steel bars embedded in early age concrete under biaxial lateral pressures at low curing temperatures

The unexpected temperature drop during the concrete curing process could degrade the concrete properties at early age, and then decrease the bond behaviour between concrete and reinforcing steel bars. To assess the effect of low curing temperature on structural safety, it is significantly important to investigate the bond behaviour of early age concrete under such extreme environmental conditions. In this study, pull-out tests were conducted on the early-age concrete specimens with embedded deformed steel bars at the low curing temperature of 0 °C and the normal temperature of 20 °C. All specimens were subjected to biaxial lateral pressures varying from 0.1 fcu to 0.4 fcu to investigate the effect of simultaneous confining pressure. The results indicated that comparing with the specimens cured at 20 °C, the bond strength for the specimens cured at 0 °C decreased significantly at earlier ages of 3 and 7 days. However, the bond strength increased steadily with the increase of the curing age. Eventually, the concrete specimens at the 28-day age reached the same bond strength for both low and normal curing temperatures. In addition, the average slip displacements corresponding to the bond strengths for the specimens at the low curing temperature was slightly lower than those at the normal curing temperature. Based on the experimental results, an empirical model of bond stress-slip relationship was proposed for the early age concrete at low curing temperatures. Comparing with other existing models, the proposed bond stress-slip relationship agreed well with the experimental results, validating its applicability for the early age concrete at low curing temperatures.

Feasibility of Bentonite as an Internal Curing Agent in Concrete

Background: There is a requirement for internal curing, especially in areas where water is scarce and where it is difficult to cure concrete due to inaccessibility of the site. About five times higher water is consumed in curing than the water used in making concrete. Furthermore, the quality of water that is to be used for these activities is required to be of a certain standard. If the requirement of water can be reduced, it becomes both economically and ecologically viable. Objective: The present research is carried out to determine the technical and economic feasibility of bentonite as an internal curing agent with properties of concrete to be used in the field. Methods: This paper compares the compressive and flexural strength parameters for standard and bentonite infused concrete and whether this can be considered as a suitable addition in concrete. The flexural strength is measured using four-point test. Both the tests are carried out in accordance with IS codes. Results: There is an increase in compressive strength for both intermittent and air curing of internally cured concrete in comparison to control concrete. Furthermore, air curing of internally cured concrete is comparable to intermittent curing of control concrete. Also, the compressive strength of intermittent curing concrete with bentonite is comparable with the strength obtained by pond curing of control concrete. Conclusion: The results indicate that bentonite can be considered as a viable addition to concrete, especially in cases of air curing. The use of bentonite is thus recommended for air curing and intermittent curing conditions.

Connections in GFRP reinforced precast concrete frames

Glass fiber reinforced polymer (GFRP) is an effective alternative reinforcing solution to tackle problems associated with steel corrosion in reinforced concrete structures located in harsh environments. However, there are multiple construction challenges when cast-in-place GFRP reinforced concrete is used. Cast-in-place concrete is both labor and time intensive on account of timely assembly of falsework and formwork as well as pouring and curing of concrete. To avoid such challenges and accelerate the construction process, GFRP reinforced precast concrete elements can be used to avoid corrosion problems, improve the quality of the construction and reduce the associated risk and total cost. While GFRP reinforced precast concrete elements exhibit behavior comparable to those reinforced with steel, research on connections between precast elements is limited. This study aims to investigate the performance of bent cap connections for GFRP precast concrete elements for applications in bridge and jetty structures. An experimental investigation was designed and conducted on a large-scale concrete frame constructed out of GFRP reinforced precast concrete elements with four different types of pocketless connections. The effectiveness of using epoxy resin rather than conventional cement grout to accelerate the construction process was investigated. Also investigated were the effect of pre-stressing, the number of connecting reinforcement elements, and the type of reinforcement (i.e. bars and bolts). The frame was subjected to cyclic lateral loading and was tested in two stages. Results and discussion on the general behavior, failure modes, energy dissipation, damping ratio and ductility were presented. The results of the pocketless test frame were also compared with a similar frame tested previously by the same research group where pocket connections were used to transfer moment between the beam and column members. The results showed that using connecting bars/bolts in pocketless connections outperform the behavior of pocket connections. This study concluded that avoiding pockets and providing the integrity of the beam-column joint through bolt/bar connection can improve the general performance of the beam-column connection compared to connections with pockets. This method also increases the speed of construction and simplifies the manufacturing procedure.

Effects of isothermal microwave curing on steel fibre-reinforced reactive powder concrete: Strength, microstructure and hydration products

A combined application of microwaving curing and reactive powder concrete (RPC) may provide an accelerated development of outstanding mechanical and physical properties, which has great potential to improve the quality and efficiency of production. In this work, a custom-made microwave oven was used to isothermally cure RPC with steel fibre reinforcement at 40 °C, 60 °C and 80 °C for 30 min. Compared to phased nonisothermal microwave curing, the isothermal microwave curing is equally effective, yet more energy efficient to operate and easier to control. The microwave-cured specimens at 1 day gained up 72.0% and 127.6% of the 28 days compressive and flexural strength achieved with standard curing, respectively. The acceleration rates varied with material characteristics and initial temperatures. The characterisation data obtained from STA, XRD and SEM-EDS analysis indicated that the beneficial effects of microwave curing temperature on strength development were due to the accelerated cement hydration and pozzolanic reaction of silica fume. The products resulting from this acceleration strengthened the interfacial zone between hydrated regions and aggregates, and the interfacial zone between the cement and silica fume. Besides C-S-H, AFm, AFt, CH, CC-, Al-tobermorite, a CO32−-contained fukalite-like phase was found to be formed, which may be produced by the pozzolanic reaction of silica fume at the expense of calcium carbonate under microwave curing.