The effects of Cr2O3 nanoparticles on strength assessments and water permeability of concrete in different curing media

In this study, the effect of limewater on strength assessments and percentage of water absorption of concrete incorporating Cr₂O₃ nanoparticles has been investigated. Portland cement was partially replaced by Cr₂O₃ nanoparticles with the average particle size of 15 nm and the specimens were cured in water and saturated limewater for specific ages. The results indicate that Cr₂O₃ nanoparticles up to 2.0 wt% could produce concrete with improved strength and water permeability when the specimens cured in saturated limewater while this content is 1.0 wt% for the specimens cured in tap water. Although the limewater reduces the strength of concrete without nanoparticles when compared with the specimens cured in water, curing the specimens bearing Cr₂O₃ nanoparticles in saturated limewater results in more strengthening gel formation around nanoparticles causing improved permeability together with high strength. In addition, Cr₂O₃ nanoparticles are able to act as nanofillers and recover the pore structure of the specimens by decreasing harmful pores. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all indicate that Cr₂O₃ nanoparticles could improve mechanical and physical properties of the specimens.     

Improvement compressive strength of concrete in different curing media by Al2O3 nanoparticles

In the present work, the effect of curing medium on microstructure together with physical, mechanical and thermal properties of concrete containing Al₂O₃ nanoparticles has been investigated. Portland cement was partially replaced by Al₂O₃ nanoparticles with the average particle size of 15 nm and the specimens were cured in water and saturated limewater for specific ages. The results indicate that Al₂O₃ nanoparticles up to maximum of 2.0% produces concrete with improved compressive strength and setting time when the specimens cured in saturated limewater. The optimum level of replacement for cured specimens in water is 1.0 wt%. Although the limewater reduces the strength of concrete without nanoparticles when it is compared with the specimens cured in water, curing the specimens bearing nanoparticles in saturated limewater results in more strengthening gel formation around Al₂O₃ nanoparticles causes more rapid setting time together with high strength. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all indicate that Al₂O₃ nanoparticles could improve mechanical and physical properties of the specimens.     

Influence of 15 and 80 nano-SiO2 particles addition on mechanical and physical properties of ternary blended concrete incorporating rice husk ash

This study demonstrates the effects of SiO₂ nanoparticles as additives with two different sizes of 15 and 80?nm on compressive strength and porosity of rice husk ash (RHA) blended concrete. Up to 20% of ordinary Portland cement (OPC) was replaced by RHA with average particle size of 5 micron. Also, SiO₂ nanoparticles were added to the above mixture at four different weight percentages of 0.5, 1.0, 1.5 and 2.0 and cured in lime solution. The results indicated that compressive strength of Portland cement–nano SiO₂–rice husk ash (PC–NS–RHA) ternary blended concrete was considerably increased. Moreover, the total amount of porosity decreased to a minimum with respect to the control concrete. This improvement was observed at all the curing ages and replacement levels, but there was a gain in the optimal point with 20% of RHA plus 2% of 80?nm SiO₂ particles at 90 days of curing.     

Enhancement of recycled aggregate properties by accelerated CO2 curing coupled with limewater soaking process

Strengthening the attached old cement mortar of recycled concrete aggregate (RCA) is a common approach to enhance the RCA properties. Accelerated CO₂ curing has been regarded as an alternative way to enhance the properties of RA. However, the improvement of the properties of RCA was limited by the shortage of reactive components in the old cement mortar available for the carbonation reactions. In this study, a CO₂ curing process associated with a limewater saturation method was performed cyclically on cement mortar samples, aiming to enhance the properties of cement mortars via artificially introducing additional calcium into the pores of the cement mortars. The results indicated that the adopted treatment method promoted the level of carbonation which was demonstrated by higher CO₂ uptake by the limewater saturated cement mortar when compared to that without limewater treatment. After 3-cycles of limewater-CO₂ treatment, the density of the cement mortar slightly increased by 5.7%, while the water absorption decreased by over a half. For mechanical properties, the compressive and flexural strength were increased by 22.8% and 42.4%, respectively. Compared to the untreated cement mortar samples, the total porosity of cement mortar was reduced by approximately 33% and the densified microstructure therefore resulted in a higher microhardness.     

Effects of Fe2O3 Nanoparticles on Water Permeability and Strength Assessments of High Strength Self-Compacting Concrete

In this work,compressive,flexural and split tensile strength together with coefficient of water absorption of high performance self-compacting concrete containing different amount of Fe2O3 nanoparticles have been investigated.The strength and the water permeability of the specimens have been improved by adding Fe2O3 nanoparticles in the cement paste up to 4.0 wt%.Fe2O3 nanoparticle as a foreign nucleation site could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount especially at the early age of hydration and hence increase the strength of the specimens.In addition,Fe2O3 nanoparticles are able to act as nanofillers and recover the pore structure of the specimens by decreasing harmful pores to improve the water permeability.Several empirical relations have been presented to predict the flexural and the split tensile strength of the specimens by means of the corresponding compressive strength at a certain age of curing.Accelerated peak appearance in conduction calorimetry tests,more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results indicate that Fe2O3 nanoparticles up to 4 wt% could improve the mechanical and the physical properties of the specimens.     

Water absorption control of ternary blended concrete with nano-SiO2 in presence of rice husk ash

In the current study, the effects of SiO₂ nanoparticles as additive with two different sizes of 15 and 80?nm on water absorption of rice husk ash (RHA) blended concrete have been investigated. Concrete samples were prepared by replacing 10, 15 and 20?wt% of cement with RHA and 0.5, 1.0, 1.5 and 2.0% of cement with SiO₂ nanoparticles followed by curing in lime solution for 7, 28 and 90?days. The results indicated that the resistance to water absorption of Portland cement?Cnano SiO₂?Crice husk ash (PC?CNS?CRHA) ternary blended concrete was considerably improved with respect to the control concrete. This improvement was observed at all curing ages and replacement levels but the optimal point was reached for 20% of RHA incorporating 2% of 80?nm SiO₂ particles at 90?days of curing. Fast formation of C?CS?CH gel in the presence of ultra high active nano-sized SiO₂ and micron level RHA particles together with their high filler effect may result in a continuous cement paste with the lowest weak zones. It has been concluded that the use of novel ternary blended concrete (PC?CNS?CRHA) provides significant reduction in the water absorption of concrete.     

Experimental investigation of the size effects of SiO2 nano-particles on the mechanical properties of binary blended concrete

In the current study, the size effects of SiO₂ nano-particles on compressive, flexural and tensile strength of binary blended concrete were investigated. SiO₂ nano-particles with two different sizes of 15 and 80 nm have been used as a partial cement replacement by 0.5, 1.0, 1.5 and 2.0 wt.%. It was concluded that concrete specimens containing SiO₂ particles with average diameter of 15 nm were harder than those containing 80 nm of SiO₂ particles at the initial days of curing. But this condition was altered at 90 days of curing. Also from the viewpoint of free energy, it can be concluded that the C–S–H gel formation around the particles with average diameter of 15 nm was more at the primary days of curing. This can be as a result of more nucleation sites that causes acceleration in early age strength. On the other hand, the growth probability of C–S–H gel around the 80 nm particles was more at 90 days of moist curing. This is due to the fact that the nucleus of strengthening gel could simply reach to the critical volume of nucleation that causes increase in the strength.     

Effect of curing methods on strength and durability of concrete under hot weather conditions

This paper reports the results of a research study conducted to evaluate the effect of curing methods on the mechanical properties of ordinary Portland cement (OPC) and Silica Fume Cement (SFC) concretes. Slab and beam specimens were prepared and cured by covering them with wet burlap or applying a curing compound under field conditions. Four types of curing compounds, namely water-, acrylic-, and bitumen-based and coal tar epoxy, were applied on the concrete specimens. The curing compounds were applied immediately after casting or after an initial period of burlap curing. The effect of the selected curing regime on the properties of OPC and SFC concrete specimens was evaluated by measuring compressive strength, water-absorption and chloride permeability. The strength and durability characteristics of both OPC and SFC concrete specimens cured by applying the selected curing compounds were similar or better than that of concrete specimens cured by covering with wet burlap. Though no significant change in strength could be noted due to the curing methodology; however, its effect was noticeable on the durability. The best performance was shown by concrete specimens cured by applying the bitumen-based curing compound followed by those cured by applying coal tar epoxy, acrylic-based or water-based curing compound. The initial period of water curing, prior to the application of the curing compound, was also noted to be beneficial in increasing the durability of concrete.     

Materials characteristics affecting CO2 curing of concrete blocks containing recycled aggregates

In order to enhance the CO₂ curing efficiency of concrete block prepared with recycled aggregates, several material characteristics of the concrete block including moisture content, bulk density, aggregate to cement ratio, recycled aggregate content and types of binders, were studied experimentally to assess their effects on the CO₂ curing process. The results indicated that, during 2 h of CO₂ curing period, the moisture content and aggregate to cement ratio of the prepared blocks had significant effects on the CO₂ curing degree and the compressive strength. Appropriate pre-drying of the block specimens before CO₂ curing enabled the maximum curing degree, and the compressive strength attained was comparable or superior to that of the 6 h steam cured blocks. The bulk density and recycled aggregate content of the prepared blocks would also influence the CO₂ curing degree, but their effects on compressive strength were more complex. It was confirmed that the presence of recycled aggregate in the concrete blocks can promote the CO₂ curing efficiency.     

A study on durability properties of high-performance concretes incorporating high replacement levels of slag

This paper presents an experimental study of combined effects of curing method and high replacement levels of blast furnace slag on the mechanical and durability properties of high performance concrete. Two different curing methods were simulated as follows: wet cured (in water) and air cured (at 20°C and 65% RH). The concretes with slag were produced by partial substitution of cement with slag at varying amounts of 50–80%. The water to cementitious material ratio was maintained at 0.40 for all mixes. Properties that include compressive and splitting tensile strengths, water absorption by total immersion and by capillary rise, chloride penetration, and resistance of concrete against damage due to corrosion of the embedded reinforcement were measured at different ages up to 90 days. It was found that the incorporation of slag at 50% and above-replacement levels caused a reduction in strength, especially for the early age of air cured specimens. However, the strength increases with the presence of slag up to 60% replacement for the 90 day wet cured specimens. Test results also indicated that curing condition and replacement level had significant effects on the durability characteristics; in particular the most prominent effects were observed on slag blended cement concrete, which performed extremely well when the amount of slag used in the mixture increased up to 80%.     

Effect of curing parameters on CO2 curing of concrete blocks containing recycled aggregates

In this study, a CO₂ curing process was adopted in order to promote rapid strength development of concrete blocks containing recycled aggregates. The influence of several factors associated with the curing conditions on the curing degree and compressive strength of the concrete blocks were investigated, including curing time, temperature, relative humidity, pressure and post-water curing after the pressurized CO₂ curing (PCC) process. In addition a flow-through CO₂ curing (FCC) method at ambient pressure was also used. The results of the PCC experiments showed that, considerable curing degree and compressive strength were attained during the first 2 h of CO₂ curing, and a prolonged curing time yielded slower gains. The variations of temperature from 20 °C to 80 °C and relative humidity from 50% to 80% had limited impacts on PCC; but the effects of CO₂ gas pressure on the curing degree and compressive strength were more pronounced. The post-water curing after pressurized CO₂ curing allowed the concrete blocks to attain further strength gain but its effectiveness was inversely proportional to the CO₂ curing degree already attained. The FCC experimental results indicated that although a lower curing degree and slower strength development at the early age were observed, after 24 h of curing duration, they were comparable to those obtained by the PCC method. To assess the thermal stability of the concrete blocks, the optimum CO₂ curing regime was adopted for preparing the concrete blocks with recycled aggregates, and the CO₂ cured specimens exhibited better fire resistance than the water-cured ones at 800 °C.     

Effect of further water curing on compressive strength and microstructure of CO2-cured concrete

This study aims to investigate the effects of further water curing on the compressive strength and microstructure of CO₂-cured concrete. The results showed that concrete with a residual w/c ratio of 0.25 showed the most rapid strength development rate upon further water curing due to hydration of uncarbonated cement particles. Thermogravimetric, IR-spectrophotometric and scanning electron microscope examinations indicated that further hydration of the cement particles could form C-S-H gel and ettringite crystals. The results showed that the calcite formed during the initial CO₂ curing was consumed during the further hydration of C₃A, and produced calcium monocarbonaluminate hydrate. Also, Ca(OH)₂ was not detected due to its reaction with the formed silica gel. Mercury intrusion porosimetry test results indicated that the porosity and pore size of the CO₂ cured mortar decreased further after water curing.     

Influence of steam curing on the properties of concretes incorporating metakaolin and silica fume

In this paper, influence of steam curing on the compressive strength, ultrasonic pulse velocity, water sorptivity, chloride ion permeability, and electrical resistivity of metakaolin and silica fume blended concretes were investigated. A total of seven mixtures containing various combinations of Portland cement (PC), silica fume (SF), and metakaolin (MK) were produced with 400 kg/m³ of total cementitious materials content and with a constant water/binder ratio of 0.44. For each mixture, concrete samples were either standard-cured in water at 23°C or steam-cured at 70°C maximum temperature over 17 h curing period. Test results revealed that steam curing enhanced the 1-day compressive strength and ultrasonic pulse velocity while leading to reduced long term strength in line with earlier findings. At the end of the water sorptivity, chloride ion permeability, and electrical resistivity tests, it was found that the steam-cured concretes had higher water sorptivity and chloride ion permeability, and lower electrical resistivity values compared to the standard cured specimens. Use of SF and MK as cementitious materials remarkably decreased the water sorptivity and chloride ion permeability of concretes, irrespective of the curing condition.     

Internal curing of Class-F fly-ash concrete using high-volume roof-tile waste aggregate

The aim of this study was to investigate the effect of a high volume of roof-tile waste coarse aggregate (5–13 mm) as an internal curing agent on the compressive strength, modulus of elasticity, pore structure, and hydration and pozzolanic reactions in paste of fly-ash concrete with a low water-to-binder ratio of 0.30. The fly-ash concrete specimens in which the replacement ratio of cement by Class-F fly ash was 40% by mass and that of normal coarse aggregate by roof-tile waste aggregate was 40% by volume, were cured up to 728 days. Internal curing with roof-tile waste aggregate increased the compressive strength of the fly-ash concrete by 8.4–16.5% and decreased the modulus of elasticity by 4.9–12.8%. The use of a high volume of waste aggregate decreased the volume of the capillary pores in the 0.01–10 µm range and the volume proportion of the 0.02–0.33-µm pores after 28 days, but increased the volume proportion of 0.003–0.02-µm pores slightly at 7 days and significantly up to 728 days, and the consumption of Ca(OH)₂ in the fly-ash concrete. This roof-tile waste aggregate can be used as an internal water reservoir to increase the compressive strength and to improve the pore structure of concrete with a high-volume (40%) replacement of Class-F fly ash.     

Styrene–butadiene latex modified calcium aluminate cement mortar

This paper investigates properties of calcium aluminate cement (CAC) mortar modified with the styrene–butadiene-rubber (SBR) latex. This material may be advantageously applied as a rapid repair mortar. Mortar specimens were prepared with constant water-to-cement mass ratio; polymer solid content of latex was varied from 0% to 9%, and Li₂CO₃ was investigated as an accelerator. Specimens were treated at different curing conditions: 1, 7 days and transformation of metastable hydration products at 70 °C. The heat of hydration evolution of mortar specimens was measured by means of a self adopted isoperibol calorimeter.The measurement results indicate that SBR latex improves workability of fresh state mortar and retards nucleation and growth of hydration products. Due to polymer coagulation process and co-matrix formation permeability, stiffness and compressive strength decrease while adhesion strength to old concrete substrate, and flexural strength increase with amount of added latex.     

Compressive strength of mortar containing natural pozzolan under various curing temperature

A first set of mortar specimens was made with 0%, 10%, 20%, 30% and 40% of natural pozzolan replacement and cured under constant curing temperature of 20, 40 and 60 °C with saturated humidity. The second set incorporating only 20% of natural pozzolan was exposed to elevated temperatures for 1, 3 and 7 days and then cured in saturated environment under a temperature of 20 °C. This paper presents the experimental results of the mortar properties such as the ultimate strength, the half age of strength and the activation energy. The introduction of the pozzolan enhances the ultimate compressive strengths and increases the activation energy which indicates the slow reactivity. The effect of the temperature on the ultimate strengths is evaluated by a new model. By using the equivalent time method, we could estimate the strength at 28 and 90 days of the second set mortar. This method satisfactorily predicts the strength of concrete cured at any temperature history.     

Effects of CuO nanoparticles on compressive strength of self-compacting concrete

In the present study, the compressive strength, thermal properties and microstructure of self-compacting concrete with different amounts of CuO nanoparticles have been investigated. CuO nanoparticles with an average particle size of 15 nm were added to self-compacting concrete and various properties of the specimens were measured. The results indicate that CuO nanoparticles are able to improve the compressive strength of self-compacting concrete and reverse the negative effects of superplasticizer on compressive strength of the specimens. CuO nanoparticles as a partial replacement of cement up to 4 wt.% could accelerate C–S–H gel formation as a result of the increased crystalline Ca(OH)₂ amount at the early ages of hydration. Increasing CuO nanoparticle content to more than 4 wt.%, causes reduced compressive strength because of unsuitable dispersion of nanoparticles in the concrete matrix. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all indicate that CuO nanoparticles up to 4 wt.% could improve the mechanical and physical properties of the specimens. Finally, CuO nanoparticles improved the pore structure of concrete and caused shifting of the distributed pores from harmless to low harm.     

Improvement of epoxy resin properties by incorporation of TiO2 nanoparticles surface modified with gallic acid esters

Epoxy resin/titanium dioxide (epoxy/TiO₂) nanocomposites were obtained by incorporation of TiO₂ nanoparticles surface modified with gallic acid esters in epoxy resin. TiO₂ nanoparticles were obtained by acid catalyzed hydrolysis of titanium isopropoxide and their structural characterization was performed by X-ray diffraction and transmission electron microscopy. Three gallic acid esters, having different hydrophobic part, were used for surface modification of the synthesized TiO₂ nanoparticles: propyl, hexyl and lauryl gallate. The gallate chemisorption onto surface of TiO₂ nanoparticles was confirmed by Fourier transform infrared and ultraviolet–visible spectroscopy, while the amount of surface-bonded gallates was determined using thermogravimetric analysis. The influence of the surface modified TiO₂ nanoparticles, as well as the length of hydrophobic part of the gallate used for surface modification of TiO₂ nanoparticles, on glass transition temperature, barrier, dielectric and anticorrosive properties of epoxy resin was investigated by differential scanning calorimetry, water vapor transmission test, dielectric spectroscopy, electrochemical impedance spectroscopy and polarization measurements. Incorporation of surface modified TiO₂ nanoparticles in epoxy resin caused increase of glass transition temperature and decrease of the water vapor permeability of epoxy resin. The water vapor transmission rate of epoxy/TiO₂ nanocomposites was reduced with increasing hydrophobic part chain length of gallate ligand. Dielectric constant of examined nanocomposites was influenced by gallate used for the modification of TiO₂ nanoparticles. The nanocomposites have better anticorrosive properties than pure epoxy resin, because the surface modified TiO₂ nanoparticles react as oxygen scavengers, which inhibit steel corrosion by cathodic mechanism.     

Effects of CuO Nanoparticles on Microstructure,Physical,Mechanical and Thermal Properties of Self-Compacting Cementitious Composites

In the present study,split tensile strength of self-compacting concrete with different amount of CuO nanoparticles has been investigated.CuO nanoparticles with the average particle size of 15 nm were added partially to self compacting concrete and split tensile strength of the specimens has been measured.The results indicate that CuO nanoparticles are able to improve the split tensile strength of self compacting concrete and recover the negative effects of polycarboxylate superplasticizer on split tensile strength.CuO nanoparticle as a partial replacement of cement up to 4 wt% could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount at the early ages of hydration.The increase of the CuO nanoparticles more than 4 wt% causes the decrease of the split tensile strength because of unsuitable dispersion of nanoparticles in the concrete matrix.Accelerated peak appearance in conduction calorimetry tests,more weight loss in thermogravimetric analysis and more rapid appearance of related peaks to hydrated products in X-ray diffraction(XRD) results all also indicate that CuO nanoparticles up to4 wt% could improve the mechanical and physical properties of the specimens.Finally,CuO nanoparticles could improve the pore structure of concrete and shift the distributed pores to harmless and few-harm pores.     

Effects of super plasticizer and curing conditions on properties of concrete with and without fiber

In this study, effects of super plasticizer (SP) and curing conditions on properties of concrete with and without fiber were investigated. In the concrete mixtures, Portland cement, artificial aggregate, SP and steel fibers were used. SP in concrete mixtures was used with ratios of 1.0%, 1.5%, and 2.0% by weight of cement and so C25 concrete was produced with and without fiber. Specimens were cured under two different curing conditions being continuous moist curing and open-air curing. Produced concrete with and without fiber were compared with each other as well as with Portland cement concrete. The highest compressive and flexural strength were obtained with 1.0% and 1.5% SP fiber reinforced concrete, respectively.