Effect Of Different Curing Regimes Research Articles

Effect of curing regimes on mechanical properties and microstructure of engineered cementitious composites with full desert sand

To establish a curing regime that facilitates the rapid enhancement and stable progression of early-age strength and tensile ductility in engineered cementitious composites with full desert sand (DSECC), aligning with production efficiency, this study examines the effects of different curing regimes (standard curing, natural curing, 20℃ water curing, and 90℃ water bath curing) on DSECC 's the mechanical properties and microstructure. The findings indicate that 90℃ water bath curing is beneficial to enhance the mechanical properties of DSECC, and its early 7 days strength and tensile deformation capacity (up to 7.05 %) can reach or exceed the standard curing 28 days level. In the uniaxial tensile test, samples cured in 20℃ water exhibit increased crack widths and reduced crack numbers, resulting in a sharp decline in the ultimate tensile strain from 4.96 % at 14 days to 1.57 % at 28 days. Natural curing leads to regression in strength at 28 days. The microstructure analysis revealed that 90℃ water bath curing fostered the development of high-density C-S-H gel and the dissolution of desert sand, while preserving the integrity of the fibers, enhancing the fiber-matrix interface transition zone (ITZ). The pore characteristic parameters under 90℃ water bath curing are superior, which has a notable refinement of the DSECC matrix's pore size. 20℃ Water curing can make up for the defects caused by desert sand and improve the compactness of matrix-aggregate ITZ. Natural curing yields the lowest degree of matrix hydration, with porosity reaching as high as 41.90 %, and pores smaller than 50 nm accounting for only 8.97 %.

Estimation of stress–strain constitutive model for ultra-high performance concrete after high temperature with an deep neural network based method

In order to better study and analyze the residual compressive behavior and stress–strain curve relationships of ultra-high performance concrete (UHPC) materials after high temperatures, high-temperature tests and uniaxial compression tests were carried out on 144 specimens in the temperature range of 20 °C-900 °C in this paper. The effects of different curing regimes and cooling regimes on the mechanical properties, apparent characteristic and stress–strain curves of UHPC after experiencing different temperatures were investigated respectively. As the target temperature increased, the stress–strain curves of all UHPC specimens gradually tended to be flatten, the peak point of the curve shifted to the right, the peak strain increased sharply, and the elastic modulus and proportional limits gradually decreased. The compressive strength and modulus of toughness of the UHPC specimens both increased and then decreased as the target temperature increased, with a critical temperature of 300 °C and 500 °C respectively. The Poisson's ratio of the UHPC specimens decreased and then increased as the target temperature increased, with a critical temperature of 500 °C. In addition, based on the experimental results, a Deep Neural Network (DNN) model with four hidden layers and 100 neurons in each layer was constructed to predict the complete residual stress–strain response of UHPC materials after high temperature. The training and validation of the DNN model was completed by pre-processing and segmenting the original dataset with the help of Pytorch deep learning libraries. The DNN model predicts stress–strain curves that are in excellent agreement with the UHPC test curves.

Influence of different curing regimes and accelerated carbonation on the physical, mechanical, and aging performances of fiber cement

The curing process in fiber cement is essential to improving the characteristics of the fiber-matrix interface, physic-mechanical performance, and durability. This work studied the effect of different curing regimes and accelerated carbonation on fiber cement to optimize these materials' production stages and physic-mechanical performance. The fiber cement flat sheets were produced with 10% bleached eucalyptus pulp by slurry-dewatering method to reproduce the commercial Hatschek process. Carbonated and non-carbonated samples were assessed at different regimes and curing ages to provide a comparative parameter. Thermal curing at 60 °C (7 days) and wet curing (28 days) was carried out after carbonation as supplementary curing. The accelerated carbonation was performed in a climatic chamber at 60 °C, 90% RH, and 20% CO2 concentration. Accelerated aging trials were also conducted for durability evaluation. X-ray diffraction, TGA, and scanning electron microscopy analyses determined the mineralogical composition, chemical components, and fiber cement microstructure. Mechanical results presented an average increase of 33% in resistance of carbonated samples compared to non-carbonated fiber cement. Additional curing increased the materials' hydration potential and demonstrated an 11% increase in calcium carbonate amounts. However, there was no statistically significant difference in fiber cement’ physic-mechanical performance with additional curing. The carbonated samples without supplementary curing presented a fiber-matrix interface like that observed in other curing regimes, even after being subjected to a shorter curing time (3 days) and accelerated aging cycles. The accelerated carbonation process enables the materials’ production at reduced ages, achieving physic-mechanical performance and durability like materials produced at more advanced ages with conventional curing regimes.

Study on the mechanical and microscopic properties of steel fiber reinforced reactive powder concrete under different curing methods

In order to investigate the effects of different curing regimes on the mechanical properties and hydration products of micro steel fiber (MSF) reinforced reactive powder concrete (RPC), three curing methods were selected: spraying curing (SPC), standard curing (SC) and (90 °C hot water + spray) curing (H + SPC). The variation rules of MSF content and age on the compressive and splitting tensile strength of RPC were analyzed, and the MSF strengthening mechanism and microscopic morphology were studied using scanning electron microscopy and X-ray diffraction microscopy techniques. Prediction models were subsequently developed for 28-day compressive and splitting tensile strength of micro steel fiber reinforced reactive powder concrete (MSF-RPC). The experimental results showed that the mechanical properties of RPC were significantly improved due to the incorporation of MSF. Under the three curing regimes, the optimal fiber volume content of MSF-RPC was 1.65%, with the improvement rates in 28-day compressive strength of MSF-RPC under SPC, SC, and H + SPC to be 33.38%, 32.22%, and 30.65%, respectively, compared with that of plain RPC. The corresponding improvement rates in splitting tensile strength were 236.24%, 211.29%, and 238.66%. The strength obtained under H + SPC was slightly higher than that obtained under SC, while its later growth rate was lower than that obtained under SC or SPC. Although the strength obtained under SPC was slightly lower than that obtained under SC, the engineering requirements were basically met, and SPC can be easily promoted in engineering practice.

Physico-mechanical, thermal insulation and resistance characteristics of diatomite and attapulgite based geopolymer foam concrete: Effect of different curing regimes

This study investigated the physicomechanical, durability and microstructure characteristics of geopolymer foam concrete (GFC) with a unit weight of less than 1500 kg/m3produced using attapulgite and diatomite. In the blends, as the main binder was used 10, 20 and 40% attapulgite instead of ground blast furnace slag (GBFS). In addition, 30, 40 and 50 kg/m3foam were used in the blends. Three alternative curing methods were used on GFC: steam (80 °C), water (∼22 °C), and an oven (80 °C). Thermal curing regimens last 24 h at a temperature of 80 °C. The blends’ porosity ranges from 36.8 to 53.3%, while their levels of water absorption range from 32.5 to 49.4%. Unit weights of hardened GFC samples range from 475 to 1226 kg/m3. On the 28th day, after applying the steam curing to blends with a 30 kg/m3foam dosage, the compressive strength is greater than 5 MPa. After 900 °C heat treatment (elevated temperature effect), a blend with a foam dosage of 30 kg/m3and 40% attapulgite produced compressive strengths of greater than 4 MPa. The blends’ depths of water penetration range from 22.1 to 27.8 mm. The drying shrinkage of the blends was increased by adding more foam and attapulgite. GFC’s thermal conductivity coefficient varies from 0.134 to 0.354 W/m.K. Increasing the attapulgite and foam decreased the thermal conductivity coefficient. Reaction products such as CASH and NASH gels were observed in SEM examinations. As a result, it has been determined that the most suitable results (In terms of physico-mechanical, thermal insulation and strength Properties) can be obtained if steam curing is applied in blends with 20% attapulgite and 30 kg/m3foam dosage.

Effect of curing regime on the immobilization of municipal solid waste incineration fly ash in sustainable cement mortar

Stabilizing/solidificating municipal solid waste incineration fly ash (MIFA) with cement is a common strategy, and it is critical to study the high-value utilization of MIFA in ordinary Portland cement (OPC) components. With this aim, binary-binding-system mortar was produced by partially replacing OPC (∼50%) with MIFA, and the effects of different curing regimes (steam curing and carbonation curing) on the properties of the cement mortar were studied. The results showed that the setting time of the cement paste was shorten with the increase of MIFA content, and steam curing accelerated the hardening of the mixture. Although the incorporation of MIFA reduced the strength of the mortar, compared to conventional curing method, steam curing and carbonation curing increased the 3-d strength of the mortar. For high-volume MIFA mortars, the CO2-cured samples had the highest long-term strength and lowest permeability. The incorporation of MIFA increased the initial porosity of the mortar, thereby significantly increasing the carbonation degree and crystallinity of the reaction product - CaCO3. Steam curing also further narrowed the difference in the hydration degree between MIFA-modified sample and plain paste, which may be due to the enhanced hydraulic reactivity of MIFA at high temperatures. Although the incorporation of MIFA increased the porosity of the mortar, this waste-derived SCM refined the bulk pore structure and decreased the interconnected porosity. Additionally, the heavy metal leaching contents of MIFA-modified mortars were all below 1%, which meet the requirements of Chinese standards. Compared with standard curing, steam curing and carbonation curing made the early-age and long-term performance of MIFA-modified mortar better, which can promote the efficient application of MIFA in OPC products.

EFFECT OF DIFFERENT CURING REGIMES ON CAPILLARITY OF CONCRETE INCORPORATING LOCAL MATERIALS

This paper reports an experimental study to investigate the effect of different curing regimes on the capillary water absorption (CWA) characteristics of concrete produced with locally available materials. Mechanical (compressive strength) and nondestructive test (ultrasonic pulse velocity) of concrete were also investigated. The engineering properties were conducted on concrete under three different curing regimes at different curing times of 2, 7 and 28 days. The three different curing conditions were water curing, dry curing and gunny-covered curing. According to the results obtained concrete under water curing condition demonstrated lower capillary water absorption (CWA) at 2 and 7 days ages and concrete under gunny-covered condition demonstrated lower CWA at 28 days age compared with the other curing conditions. It is interesting to see that the compressive strength (38 MPa) of concrete was almost the same at 28 days age under gunny-covered and water curing conditions.

Drying Shrinkage Performance of Ambient Cured Blended Alkali-Activated Concrete

The environmental burden due to the production and use of Ordinary Portland Cement(OPC) has become significant in terms of resource use and atmospheric emissions. Alkali-activatedbinders have gained significant attention in recent years as a possible alternative to OPC. Concreteundergoes physical and chemical changes through its lifetime. These changes affect propertiesresulting in either increase or decrease of performance and serviceability. Concrete contracts due tothese changes leading to shrinkage. Shrinkage induces tensile stresses within the members, whichleads to a tendency of cracking, resulting in compromised durability. Shrinkage behavior analysis ofAlkali-Activated Concrete (AAC), without any external loading, is crucial to assess as there is limiteddata available. To further test for shrinkage under restraint conditions, mix development of AAC isnecessary. Mechanical properties and drying shrinkage potential of AAC are evaluated and comparedwith OPC concrete. Basic properties assessed to understand the performance of AAC are compressivestrength, splitting tensile strength and free drying shrinkage. Drying shrinkage test is performed as perASTM C157 for 90 days. Furthermore, the effect of different curing regimes (dry curing, three daysmoist curing, and seven days moist curing) on the mechanical properties and shrinkage is evaluated.The results show that drying shrinkage of AAC exhibit similar behavior to that of OPC concrete whilehaving better early-age strength under moist curing regimes.

UTILIZATION OF PUMICE OF BURDUR REGION AND ZEOLITE OF BIGADIC, BALIKESIR REGION AS FINE AGGREGATE IN CONSTRUCTION MATERIALS

Volcanic originated pumice and zeolite aggregates have low density owing to their considerable porous structure. Porosity is usually correlated with insulation properties. In order to examine the effects of this lightweight aggregates on dead load of structure and insulation properties of standard construction materials, samples were produced by using pumice and zeolite at varying percentages by volume and control samples were manufactured with crushed sand. The samples were exposed to normal (standard) curing, hot water curing and steam curing to observe the effect of different curing regimes on their behavior. Bulk density and thermal conductivity tests were carried out on samples. Both bulk density and thermal conductivity values of the lightweight mortar samples were smaller than those of control sample. Besides, chemical compositions of aggregates and cement, analyses were also performed. Silica content of pumice and zeolite were %54,09 and %75,14 by mass respectively.

Properties of lightweight concrete made with core-shell structured lightweight aggregate

In this study, core-shell structured lightweight aggregates (CSA) were produced through the cold bonding method, by encapsulating an expanded perlite particle (as a core structure) within a shell matrix composed of cement, fly ash and expanded perlite powder. The effect of different curing regimes on the mechanical and microstructural properties of the CSA were studied. To enhance the characteristics of the aggregates produced, they were surface treated by a mixture of cement and silica fume, using two different treatment methods. Afterwards, the properties of lightweight concrete made of either CSA or expanded clay aggregate (ECA) were compared closely in terms of their potential economic and environmental benefits, in response to the high energy consumption associated with the production of ECA. The results revealed that curing at a relative humidity of 99% is the most appropriate curing method for CSA. In addition, treating the CSA surface contributes significantly to enhancing its bulk crushing strength, by about 14–18%. The findings also demonstrate the feasibility of using CSA to produce lightweight aggregate concrete, with a dry density and compressive strength ranging from 1115 to 1540 kg/m3 and from 17.9 to 25.8 MPa, respectively, with a corresponding thermal conductivity range of 0.3169–0.6660 W/m·K.

Development of multi-strength grade green lightweight reactive powder concrete using expanded polystyrene beads

In this study, a new class of green light weight reactive powder concrete (GLRPC) was developed in different strength-grades by using expanded polystyrene beads. Quartz powder was totally substituted by ground granulated blast furnace slag as an industrial waste material to develop a more cost-effective and environmentally-friendly product. Various mixtures were studied by application of expanded polystyrene beads of the size between 0.5 and 2.3 mm, CEM-II Portland cement, silica fume, GGBFS, polycarboxylate based superplasticizer and water. The effects of different curing regimes including standard water curing and heat curing at 100, 150 and 200 °C on compressive strength, water absorption, and microstructure of GLRPC were investigated. Based on the measurements, density, compressive strength and water absorption values between 1257 to 1840 kg/m3, 20.8 to 85.6 MPa, 3.47 to 0.22% for GLRPC mixtures were achieved, respectively.

Effect of different curing regimes and durations on early strength development of reactive powder concrete

The early strength development of Reactive Powder Concrete (RPC) has been investigated under different curing regimes and compared with standard water curing condition. Four different curing regimes have been considered: ambient air curing, hot air curing, hot water bath curing and accelerated curing. The effect of hot air curing on strength development of RPC at different temperatures and durations are studied in detail. The present study is focused on the effect of combined curing regimes on the early strength development of RPC. Test results indicate that, among the four different curing regimes, hot water bath curing gives higher strength. The combined curing regime has considerably enhanced the compressive strength of RPC by about 63% as is evident by the rise in compressive strength from 110MPa (standard curing) to 180MPa (combined curing). Microstructure studies were also conducted to understand the arrangements of hydrated particles and development of other secondary hydrated products under different curing conditions using scanning electron microscope and X-ray diffraction spectroscopy respectively.

Investigation on Mechanical Properties of Reactive Powder Concrete under Different Curing Regimes

Reactive Powder Concrete (RPC) is a form of Ultra High Performance Concrete (UHPC). The main constituents of RPC are cement, sand, silica fume, steel fiber and quartz powder with minimal water to binder ratio, without coarse aggregate. Due to its dense microstructure, RPC exhibit superior properties such as higher strength, durability and long term stability. Earlier researchers have produced RPC with Compressive strength up to 800 MPa and flexural strength of 75 MPa. In the present study, locally available materials are used to produce RPC of different mix proportions. The main objective is to study the effect of different curing regimes on the strength of RPC. The durability study is also carried out by way of accelerated corrosion test and acid test. Results have shown considerable enhancement in compressive strength when RPC specimen were subjected to hot air curing of different durations. RPC specimen cured under hot air curing and steam curing shown better performance compared to normal curing and air curing. Also RPC has shown better resistance to sulphate attack; further the rate of corrosion is low compared to high performance concrete.

AN EXPERIMENTAL STUDY ON SELF CURING CONCRETE USING LIQUID PARAFFIN WAX

The most regularly and abundantly used construction material is concrete because of its superior compressive strength and stability. Curing is one of the major parameter which helps in improving water retention capacity of concrete which in turn helps in developing the microstructure of the concrete. The curing involves in retaining adequate moisture content from the time of placing the concrete until final stage, at that point of time the concrete develops the satisfied properties by promoting optimum cement hydration immediately after placement. Properly cured concrete has improved durability and surface hardness, and is less permeable. Prevention of loss of moisture is important not only for strength development but also to prevent plastic shrinkage, for decreased permeability and to improve resistance to abrasion. Good and complete curing is not always possible for several reasons such as human errors, vertical members and places where there is scarcity of water. In such cases using self-curing concrete is very adaptable and helps in mitigating this problem. The basic notion of self curing concrete is to make sure that the concrete is free from water evaporation, and hence improve its water withholding capacity when compared to usual curing. Several hydrophilic materials, including polymeric glycol and paraffin wax, can act as self-curing compounds. This study investigates the role of liquid paraffin wax as a self curing agent and compares this with the effect of different curing regimes simulating traditional methods of curing. The dosage of liquid paraffin wax compound taken is 0.1%. The parameters include grade of concrete, dosage of paraffin wax, curing conditions and age of curing. The strength parameters namely compressive strength, split tensile strength and flexural strength are determined as a performance benchmark for the investigated curing compounds.

Paraffin wax as an internal curing agent in ordinary concrete

Curing of concrete involves maintaining satisfactory moisture content during early stages to develop the desired properties. Properly cured concrete has improved durability and surface hardness, and is less permeable. Prevention of loss of moisture is important not only for strength development but also to prevent plastic shrinkage, for decreased permeability and to improve resistance to abrasion. Good and complete curing is not always practical for several reasons, particularly in higher grade concretes. Using self-curing agents can solve this problem. The concept of self-curing agents is to reduce water evaporation from concrete, and hence increase its water retention capacity compared to conventional curing. Several materials, including polymeric glycol and paraffin wax, can act as self-curing compounds. This study investigates the role of paraffin wax as a self-curing agent and compares this with the effect of different curing regimes simulating traditional methods of curing. The parameters include grade of concrete, type and dosage of paraffin wax, curing conditions and age of curing. Weight loss and compressive strength are determined as a performance benchmark for the investigated curing compounds. It is found that the lower dosage (0·1%) liquid paraffin wax compounds act as the best curing compounds in higher grade concretes.

Effect of Different Curing Regimes on Shrinkage and Strength Properties of Self-Consolidating Mortars Containing Silica Fume in Different Contents

The aim of this research is to study the effect of different curing regimes on shrinkage and strength properties of self-consolidating mortars (SCM) containing silica fume in different contents. Self-consolidating mortars, as new technology products, are especially preferred for use in architectural elements and the rehabilitation and repair of reinforced concrete structures. SCM can be used in precast architectural elements or cast in place repair of reinforced concrete structures. Therefore, investigation on the effects of different curing methods on key properties of SCMs can be beneficial. The shrinkage and strength properties of SCMs produced at different replacement ratios of silica fume (SF) with cement in different curing regimes were studied, at this paper. SCM mixes were prepared in constant water/powder ratio and cured in four different regimes including water curing (WC), accelerated water curing (AWC), air curing (AC) and aluminum tape sealing (AS). A polycarboxylate-based superplasticizer (SP) was added to the mixtures at different rates by mass of the cementitious materials to have appropriate flowability. Fresh mortars workability was determined using mini slump flow and mini V-funnel tests. All SCM specimens were tested and evaluated for compressive strength, flexural strength and shrinkage. It has been found that different curing regimes have considerable effects on both shrinkage and strength properties of SCM. It can be concluded that aluminum tape sealing and accelerated water curing can be used as effective and successful curing methods particularly where the SCM is used as a repair material or in architectural elements, respectively.

Effects of different curing regimes on the compressive strength properties of self compacting concrete incorporating fly ash and silica fume

This paper presents the effect of air curing, water curing and steam curing on the compressive strength of Self Compacting Concrete (SCC). For experimental study, SCC is produced with using silica fume (SF) instead of cement by weight, by the ratios of 5%, 10% and 15%, and fly ash (FA) with the ratios of 25%, 40% and 55%. It is observed that mineral admixtures have positive effects on the self settlement properties. The highest compressive strength was observed in the concrete specimens with using 15% SF and for 28days water curing. Air curing caused compressive strength losses in all groups. Relative strengths of concretes with mineral admixtures were determined higher than concretes without admixtures at steam curing conditions.

Effects of Different Curing Regimes on Engineering Properties of Polymer-Modified Mortar

Despite the fact that polymer-modified mortar can be widely used as a material for major construction projects, the extensive use of this promising material may be hampered because of not enough published data on its durability performance. This paper, based on a laboratory program, compares the engineering properties, over different aging, of three commercial polymer-modified mortars [styrene-butadiene rubber (SBR), polyacrylic ester (PAE), and vinyl acetate-ethylene (VAE)] and unmodified conventional mortar mixes exposed to different curing conditions. The results show that the SBR mixes appeared to possess better engineering properties than the PAE and VAE mixes, and a well-designed polymer-modified mortar mix can retain its engineering properties over a long period of time.

Effect of Fiber Addition, Heat Treatment, and Preset Pressure on Mechanical Properties of Ultra-High-Strength Mortars

In this study, efforts were undertaken to produce ultra-high-strength mortars (UHSM) from conventionally available materials. Selection of mixtures and optimization of mixtures were achieved by adopting the basic principles of UHSM and through trial studies. A preliminary investigation was carried out to assess the effects of different curing regimes on the strength development of UHSM. Effects of fiber addition, heat treatment, and preset pressure on the rate of strength development of UHSM mixtures were individually assessed to better understand their benefits in the production of UHSM. Mechanical properties of the heat-treated UHSM were then investigated to determine the performance of the UHSM developed from conventional materials. Results from this study suggested that for the production of UHSM, a multiple curing regime was best suited and was then used for further studies. Data on strength development indicated that heat treatment increased the strengths by 57% to 75%. With application of preset pressure, the compressive strengths of UHSM were increased significantly by 15% to 18%. The optimum quantity of fibers to produce UHSM was found to be 2% to 3%. Effectiveness of fibers in increasing the strength of UHSM was found to be higher for heat-cured specimens than for normal water-cured specimens. The maximum target strengths obtained from the UHSM were 194 MPa, 24 MPa, and 31 MPa for compression, split tension, and flexure, respectively. The UHSM also showed improved energy absorption and toughness characteristics, especially at higher-fiber dosages.

A study of the curing of sealants used in building construction

Important material properties such as strength, elasticity, movement capability and weather resistance are developed as a sealant cures. Indeed, the magnitude of key material properties such as modulus is directly related to the level of cure. Hence it is important to appreciate the level of cure of a sealed joint when it is being tested. A review of the curing of sealants is given with some generalized cure mechanisms proposed for polysulfide, polyurethane and silicone sealants. There is generally very little published work on assessing the cure of sealants. The deficiencies in traditional methods for measuring the level of cure in polymer systems (for example, hardness and rheometry tests) when applied to sealants are outlined. Two alternative methods were used to determine the state of cure of six sealant materials: the measurement of modulus and glass transition temperature ( T g ) with cure time. The effect of different curing regimes on cure development was monitored for up to 16 weeks' cure time. The results show that both modulus and T g are useful parameters for assessing the cure level of sealants, with T g measurement being particularly elegant. Six weeks' curing appeared to be the minimum cure time necessary to provide a sufficiently high degree of cure for material testing to be performed, regardless of curing regime of sealant type used.