Air Curing Research Articles

Physico-mechanical and shielding properties of alkali-activated slag composites incorporating cement clinker aggregate: Effect of high temperature and particle size

The purpose of this research was to see how cement clinker aggregates (CCA) and curing temperature affected the physico-mechanical and shielding properties of alkali-activated composites (AAC) exposed to high temperature. The precursor used to create AAC was ground blast furnace slag (GBFS), which was activated using a solution of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH). Quarts powder with a size range of 0–0.5 mm and CCA in two different size ranges (0–4 mm and 4–8 mm) were used as fine and coarse aggregates in the fabrication of AAC. Four different AAC mixes were produced which were cured by three curing temperatures at 25 °C (air curing), 40 °C, and 80 °C for 8 h. The impacts of curing temperature and CCA size and content were examined on the AAC's flowability, compressive strength, flexural strength, porosity, dry unit weight, and water absorption and sorptivity characteristics. The high temperature performance and shielding properties of the produced blends was also assessed. Microstructure investigations of AAC mixtures produced within the scope of the study were also carried out based on FTIR and SEM. The obtained results implied that compressive strength of up to 80.80 MPa was attained with the use of CCA at curing temperature of 80 °C. The M4 containing the highest CCA content with the sizes of 4–8 mm and the lowest CCA content with the sizes of 0–4 mm exhibited the lowest strength at all curing temperatures. All AAC mixes regardless of curing temperature lost more than 60% of their initial compressive strength after 300 °C. Finally, among the AAC mixtures, whose gamma-ray shielding properties were examined in the photon energy range of 81–661 keV and whose fast neutron dose rates were determined, 0–4 mm particle size Clinker doped M1 sample showed better nuclear shielding ability compared to other mixtures studied.

Effect of curing conditions on the strength and durability of air entrained concrete with and without fly ash

In cold regions, air entrained concrete has been widely used against freeze–thaw deterioration. This paper studied the influence of curing conditions on the strength and durability of air entrained ordinary portland cement (OPC) and fly ash (FA) concrete. Four different curing conditions including standard curing (SC), air curing (AC), mild temperature curing (MC), and elevated temperature curing (EC) were utilized to cure the cast specimens. The compressive strength at 3, 7, 14, and 28 days was measured respectively. Also, the water absorption, sorptivity, air void system, as well as freeze–thaw durability after 28 days of curing were investigated. Test results suggested that AC condition impeded the strength gain of both concrete, but it affected FA concrete more than OPC concrete. EC condition improved the early-age strength while compromised the later-age strength of OPC concrete, whereas EC condition improved the compressive strength of FA concrete at both early ages and later ages. AC condition has more adverse effects on water absorption as well as sorptivity of FA concrete than those of OPC concrete. EC condition increased the water absorption and sorptivity of OPC concrete, whereas reduced the water absorption and sorptivity of FA concrete. Although the air content in fresh OPC and FA concrete were comparable, FA concrete had less proportion of microvoids (air voids smaller than 300 μm), larger spacing factor but smaller specific surface, regardless of curing conditions. EC condition caused the reduction in air content, the increase of spacing factor, and decrease of specific surface. For both OPC concrete and FA concrete, the four curing conditions produced different freeze–thaw durability factor (DF), but all the specimens passed the failure limit of 60 %. The freeze–thaw test results based on specimens under SC condition may overestimate the DF.

Effect of dosage of super absorbent polymer on self-consolidating concrete: Correlation between compressive strength and rheological properties

This research investigates the super absorbent polymer effect on self-consolidating concrete's compressive strength and rheological properties (SCC). The SCC mixes contained four different dosages of super absorbent polymer (SAP). The Rheological properties of SCC changed by adding SAP, and also workability decreased due to water absorption from the mix by dry SAP. The compressive strength of concrete increased, especially in air curing and gunny bag curing, at all curing ages but decreased in water curing. Experimental investigation measured the yield stress, plastic viscosity, slump flow and V-funnel time to assess the rheology of concrete and compressive strength in three curing regimes. In this study effect of super absorbent polymer on rheology and compressive strength of SCC in water curing, air curing, and gunny bag curing regimes has been revealed. Correlations have been found among Plastic viscosity, Yield stress, Slump flow value, V-funnel time, and compressive strength of concrete at 28 days of curing in three curing regimes.

Mechanical performance improvement of super absorbent polymer-modified concrete

In this study, a method has been developed to reduce the negative effects of superabsorbent polymers on concrete mechanical properties. The method involves concrete mixing and curing, with the concrete mixture being designed using a decision tree algorithm. Instead of the standard water curing approach, air curing conditions were used during the curing process. In addition, heat treatment was applied to reduce any possible negative effects of the polymers on the concrete's mechanical properties and to enhance their performance. The details of all these stages are presented in this method. Various experimental studies were conducted to demonstrate the validity of this method, which proved to be effective in reducing the negative effects of superabsorbent polymers on concrete mechanical properties.•The method can be used to eliminate the negative effects of superabsorbent polymers.•The proposed method yielded promising results, demonstrating that the expected level of compressive strength, modulus of elasticity and toughness in concrete can be achieved in 5-10 days instead of 28 days•The widespread use of superabsorbent polymers in the concrete industry and reinforced concrete systems can be attributed to their many benefits.

Effect of curing techniques on compressive strength of concrete

This paper presented the findings of an experimental investigation into how common Portland cement concrete develops its compressive strength in a simple setting, such as Lahore, Pakistan. Ten concrete cube specimens of mix 1:1.5:3 was prepared with water-cement ratio of 0.5 for each of the four curing techniques (air curing, water-submerged curing, polythene curing, curing by boiling) until testing ages of 3, 7, 14, 21 and 28 days when their compressive strengths were determined. The findings demonstrated that concrete specimens produced using the water-submergence technique of curing had the maximum 28-day compressive strength of 41.42MPa. The findings indicate avoiding boiling as a curing process and restricting the use of other curing techniques to a 28-day timeframe. It was determined that there is a positive link between concrete specimen curing, curing duration, and compressive strength. This study also offers details on the significance of curing and numerous different methods for carrying out the procedure on the spot.

EVALUATION OF CURING TIME FOR MICRO CONCRETE MIXES CONTAINING SILICA FUME, NANO-SILICA AND FLY ASH

Within the scope of the study, research on the use of silica fume (SF), nano silica (NS) and fly ash (FA) together or separately in the production of micro concrete is presented. It is aimed to examine the changes in mechanical properties because of water and air curing in mixtures produced using SF, FA, and NS. While cement dosage and water/binder ratio in the mixtures were chosen as 670 kg/m3 and 0.53 respectively, the amount of SF, FA and NS was limited to 150 kg/m3 in total. In the study, samples were produced using 40x40x160 mm prism molds. All samples were divided into two different groups after 7 days of water curing and water (1st group) and air (2nd group) were applied up to 56 days. Flexural and compressive strength tests were performed on the water and air cured specimens for 7-56 days and 28-56 days, respectively. In addition, the porosity and unit volume weight values of the samples were examined. The results show that both flexural and compressive strengths of micro concretes increased after 28 days thanks to water curing.

The Effect of Post-Fire Air Curing on Alkali-Activated Slag and Fly Ash Mortars

Bu çalışmada alkali ile aktive edilmiş yüksek fırın cürufu ve uçucu kül içeren harçların dayanım özelliklerine yüksek sıcaklık sonrası hava kürü koşullarının etkisi araştırılmıştır. Bu amaçla uçucu kül %0, %25, %50, %75, %100 oranlarında yüksek fırın cürufu ile ikame edilerek alkali ile aktive edilmiş harçlar üretilmiştir. Harçlarda aktivatör olarak %10 oranında Sodyum (Na) içeren sodyum metasilikat kullanılmıştır. Üretilen harçlar 24 saat 90°C ısıl küre tabi tutulmuştur. Isıl kür sonrası numuneler 400, 600 ve 800oC’de yüksek sıcaklığa maruz bırakılmıştır. Referans grubu numuneleri etüv kürü uygulandıktan sonra, birinci grup numuneler yüksek sıcaklık uygulandıktan 1 gün sonra, ikinci grup numuneler ise yüksek sıcaklık uygulandıktan 28 gün sonra ağırlık kaybı, eğilme dayanımı ve basınç dayanımı testlerine tabi tutulmuştur. Yüksek sıcaklık öncesi en yüksek basınç dayanım 75,5 MPa ile %100 cüruflu numunelerde elde edilirken en düşük basınç dayanımı 44,6 MPa ile %100 uçucu kül içeren numunelerde elde edilmiştir. Yüksek sıcaklıktan sonra 28 gün havada kür uygulanan numunelerin basınç dayanım değerleri yüksek sıcaklığa maruz kalmayan numunelerin basınç dayanım değerleri ile karşılaştırıldığında,400oC, 600oC ve 800oC’de sırasıyla en fazla %32, %64 ve %93 basınç dayanımı kaybı meydana gelmiştir. Numunelerin yüksek sıcaklık sonrası 1 ve 28 gün süreyle havada kür edilmesi, basınç dayanımlarında önemli bir değişikliğe neden olmamıştır. Yüksek sıcaklık sonrası eğilme ve basınç dayanımı kaybı hemen oluşmuş, 28 gün hava kürü ile numuneler genel olarak basınç dayanımlarını korumuşlardır.

Filler effects of CaCO3 polymorphs derived from limestone and seashell on hydration and carbonation of reactive magnesium oxide (MgO) cement (RMC)

This study investigated the influence of CaCO3 polymorphs from limestone and seashell on the hydration and carbonation kinetics of reactive MgO cement (RMC). Replacement levels at 5 and 10 wt% were adopted, and the samples were exposed to ambient curing before carbonation under 20 % CO2. The superior filler effects imparted by the limestone powder were demonstrated with an enhancement to the normalized heat flow at an early stage of hydration, leading to an increase in the compressive strength under air curing. Its nucleation effect did not lead to more brucite but involved the formation of amorphous phases, which encapsulated and passivated the MgO substrate, consequently restricting its hydration. Under carbonation, nucleation induced by both the CaCO3 forms improved the composite strengths by producing carbonation products of larger morphologies, resulting in pore filling and matrix densification. Amorphous phases of a hydromagnesite-like and fused structure were observed.

Rheological, deformation behaviors and mechanical changes of MgO-containing concretes with different strength

MgO content is of importance to the compensation feasibility and soundness of concrete, especially for concrete with different strength grades. The rheological, deformation behavior, and mechanical changes of MgO expansive agent (MEA) (5–8 wt%) in different strength grades of concrete were revealed. Results show that MEA replacement of cement makes the yield stress and plastic viscosity increasing because of the high specific surface and agglomeration of MEA. Although same quantity of Mg(OH)2 is generated, concretes with different strength grades display different expansion behaviors because of their different pore structures and Mg(OH)2 morphology. Mg(OH)2 that growing around MgO particles presents a colloidal morphology, while Mg(OH)2 that growing in the surrounding pores presents a hexagonal flake-like morphology. The restrained deformation of Grade 40 concrete with 6 wt% MEA after curing in water for 14 d increases to the maximum expansion, reaching 237 × 10−6.6 wt% MEA replacement does not affect the compressive strength and splitting tensile strength of concrete with different strength grades. However, 7–8 wt% MEA replacement reduces the splitting tensile strength of Grade 40 concrete, and the negative impact is particularly pronounced after air curing.

Properties, mineralogy and microstructure evolution of 4-year calcium silicate slag-based alkali-activated materials

Alkali-activated materials (AAMs) are considered promising alternatives to ordinary Portland cement (OPC). The long-term stability and safety of AAMs are not fully acknowledged due to the lack of sufficient studies. The AAMs were prepared with calcium silicate slag (CSS), ground granulated blast furnace slag, fly ash and liquid sodium silicate in this study. Then, the evolution of mineralogy, microstructure and mechanical properties of CSS-based AAMs cured in ambient air were investigated on a time scale of 4 years. The results showed that the continuous alkali-activation and gradual carbonation both occurred during the 4-year curing in ambient air. Despite this, the main products of 4-year CSS-based AAMs were still C(N)-(A)-S-H gels. The gel products derived from the continuous alkali-activation filled the pores and resulted in decreasing porosity. Consequently, the compressive strength of CSS-based AAMs progressively increased from 55.0 MPa at 28 days to 100.0 MPa at 4 years due to the increasing compactness of the matrix.

Studying the properties of epoxy polymer concrete reinforced with steel and glass fibers subjected to cycles of petroleum products

Petroleum products, which are widely used in technological processes, fall on concrete and reinforced concrete elements of structures and gradually impregnate them. This can have a negative impact on their reliability and mechanical safety. This paper investigates the effect of petroleum products on fiber reinforced polymer concrete (FRPC). Two types of petroleum, gasoline and gas oil, have been used. In the current work four polymer concrete mixes were used with incorporation of steel fibers (SF), glass fibers (GF), and mix of (ST+GF), in addition to polymer concrete without fibers. The polymer concrete was prepared by using epoxy resin as a binder. After 28 days of air curing, the prepared concrete was submerged in gasoline and gas oil at different periods of exposure cycles at 60, 90, 120 and 150 days. Each cycle includes two weeks of submerging and then two weeks of drying to evaluate its properties including compressive strength, splitting tensile strength, ultrasonic pulse velocity, dynamic elastic modulus and total absorption, and comparing the results with the reference samples. The results indicated that using FRPC with a mix of ST and GF gave the highest properties in comparison with other mixes. The mechanical properties improved by 15 % in comparison with the reference mix. Also, gas oil has a greater adverse effect than gasoline on FRPC. For all mixes, the gas oil led to a decrease in the compressive strength by 3 % lower than gasoline. Furthermore, most of the tested properties decreased after four exposure cycles, but despite that, the FRPC achieved higher properties in comparison with the reference mixture.

Effects of the partial replacements of Oil Palm Boiler Clinker (OPBC) on the density and compressive strength of concrete

Purpose: Oil Palm Boiler Clinker (OPBC) is a promising waste material that can be deployed toward sustainable development. Researchers have been looking into the potential of industrial waste and by-products to provide an alternative to natural stone aggregates in concrete production. This study aims to determine an OPBC concrete mix eligible for lightweight reinforced precast concrete products according to BS EN 13369:2013.
 Design/methodology/approach: The concrete mix design is determined via the trial mix method, where percentages of OPBC are varied as partial replacements in the control mix. Raw OPBC is collected from a local palm oil mill in Johor, Malaysia and is processed to be implemented in the concrete mix. Three 100mm cube samples of nine OPBC mixes and one control mix are tested and weighed on day 1, day 7, and day 28 to determine their cube compressive strength and density to BS EN 12390-3:2009. The mix that fulfils the requirements is the mix with 90% coarse clinker and 90% fine clinker, cured by the method of air curing, which achieved a cube compressive strength of 38.66N/mm2 and density of 1920kg/m3.
 Findings: In conclusion, the results show that OPBC concrete is a green alternative to standard concrete that does not differ significantly in terms of strength while offering a density reduction of as much as 16%.
 Originality/value: This paper is original
 Paper type: Research paper

Effect of freeze-thaw damage at curing time on mechanical properties of polyurethane concrete

PurposePolyurethane concrete has a high strength-to-weight ratio in the short term, and the strength-to-weight ratio stage during the maintenance period is critical. Freeze-thaw cycles have a noticeable damaging effect on the durability of polyurethane concrete. The engineering specification of polyurethane concrete with incomplete hydration reaction must be studied, as well as the development of internal structure during curing. In this paper, the polyurethane concrete tests were set up under eight distinct maintenance settings based on the climate features of the northern area and the service environment. The test results were evaluated to determine the effect of the number of early freeze-thaw cycles and the time node of early freeze-thaw cycles on the mechanical characteristics of polyurethane concrete, which revealed that the time node of freeze-thaw damage impacted the freeze-thaw resistance of polyurethane concrete susceptible to early freeze-thaw damage.Design/methodology/approachThe early-age freeze-thaw damage polyurethane concrete was experimentally studied by controlling the time node of the freeze-thaw cycle and the curing environment. The test considered the time node, frequency of freeze-thaw damage of polyurethane concrete and the influence of subsequent curing environment and observed the mass change, relative dynamic elastic modulus, relative durability index, compressive strength and apparent damage of polyurethane concrete. The early mechanical properties of polyurethane concrete were studied by analyzing the change of numerical value. The microscopic mechanism of strength formation of polyurethane concrete was analyzed by XRD, FTIR and SEM image.FindingsThe closer the time of freeze-thaw damage was to the specimen hardening, the worse the mechanical properties and structure were, according to SEM photographs. For specimens with serial number of 12-groups, its compressive strength is only 82.39% of that of the standard group, even if the curing process continues after 20 times thawing, which increased early environment exacerbate strength loss in polyurethane concrete and also reduced freeze-thaw resistance. The findings of the tests reveal that curing can restore the freeze-thaw resistance of damaged polyurethane concrete. Curing in water has a better recovery impact than curing in air; the mechanical properties can be restored by sufficient re-curing time and good re-curing conditions.Originality/valueBy studying the freeze-thaw cycle test and test results of polyurethane concrete in different curing time nodes, the relationship between the mechanical properties of polyurethane concrete and the time node, number of freeze-thaw cycles, and subsequent maintenance environment was explored. Considering the special mechanism of strength formation of polyurethane concrete, the polyurethane concrete damaged by freeze-thaw has the ability to continue to form strength under subsequent maintenance. This experimental study can provide an analytical basis for the strength formation and reconditioning of polyurethane concrete structures subjected to freeze-thaw environments during the curing time under extreme natural conditions in fall and winter in actual projects.

Low-temperature cross-linking fabrication of sub-nanoporous SiC-based membranes for application to the pervaporation removal of methanol

Separating azeotropic organic-organic mixtures using membranes is of great importance in the chemical and petrochemical industries, but remains extremely challenging because membranes must be able to withstand harsh working conditions while providing adequate permselectivity. Silicon carbide (SiC)-based membranes have attracted a great deal of interest due to their high level of structural stability, mechanical strength, and corrosion resistance. Herein is an account of the first study focused on a systematic investigation into the physicochemical and pore structural variations of polycarbosilane (PCS)-derived SiC-based membranes under different air-curing and pyrolysis temperatures. Air curing for cross-linking behavior was found to occur at temperatures as low as 150 °C, and the completion of polymer-to-ceramic conversion for PCS was observed at 750 °C. In addition, the pore structure and surface properties (hydrophilicity/hydrophobicity) of PCS membranes could be tuned by the pyrolysis temperature. PCS membranes derived from air curing at a temperature as low as 150 °C possessed sub-nanopores that ranged from 0.5 to 0.66 nm depending on the pyrolysis temperature. The formation of these sub-nanopores was attributed to sparsely cross-linked networks. Subsequently, the pervaporation (PV) performance of methanol/methyl acetate, methanol/toluene, and methanol/methyl tert-butyl ether were evaluated and discussed with respect to any effects of different pore sizes of the membranes and operating parameters. The most outstanding separation performance emerged from SiC-based membranes with a pore size of 0.50 nm that were air-cured at 150 °C and then pyrolyzed at 750 °C. The impressive PV separation capability was attributed to the surface hydrophilicity, suitable pore size, and high quality of the SiC-based membranes. Furthermore, the PV performance correlated well with single-gas permeation, suggesting that PV performance could be predicted based on single-gas permeation. The developed SiC-based membranes have excellent separation performance and are a promising candidate for the PV separation of MeOH from organic mixture systems.

Effect of post-fire curing on compressive strength of ultra-high performance concrete and mortar

• Compressive strength of both UHPC and mortar increases at 300 ℃ but decreases at higher temperature. • Post-fire water curing is more effective on recover the compressive strength of the UHPC mix and Mortar than the post-fire air curing. • Strength recovery of the Mortar is greater than that of the UHPC. • Precipitation of portlandite heals the coarsened microstructure and recovers compressive strength. This paper investigates effects of post-fire curing on strength recovery and changes in microstructure of ultra-high performance concrete (UHPC) and mortar. Specimens were heated to elevated temperatures 300, 600, and 900 °C with a heating rate of 1 °C/min. After cooling, the specimens were subjected to post-fire curing in either air or in water for 56 days. Compressive strength, X-ray diffraction (XRD), mercury intrusion porosimeter (MIP), and field emission scanning electron microscope (FESEM) tests were conducted to examine the changes at both macro and micro scale and to reveal deterioration mechanisms due to fire effect and healing mechanisms due to post-fire curing. The test results showed that compressive strength of both UHPC and mortar increased slightly after 300 °C exposure but decreased significantly at higher temperature due to the coarsening of microstructure. Post-fire curing in air showed very limited strength recovery since new curing products did not heal thermal cracks larger than 1 μm. On the other hand, curing in water led to substantial strength recovery of the mortar mix due to formation of portlandite which compactly filled the microcracks in fire-damaged samples. However, the loose ettringite phase formed in the UHPC mix did not contribute to regaining the initial compressive strength.

Study on Fresh and Hardened Properties of Nano-Concrete Under Different Curing Conditions

In the recent days usage of nano materials in concrete are responsible in creating ultra-high-performance concrete. Curing is another important strength enhancing parameter in all types of concrete. The nano concrete was achieved by replacing cement in the conventional concrete with Nano silica (NS) in the order of 0.5%, 1%, 1.5%, 2%, 2.5% and 3%. In the present study nano concrete was experimentally explored to mechanical properties like workability, Compressive Strength (CS), Flexural Strength (FS), Bond Strength (BS), Water Absorption (WA), and Thermal Conductivity (TC) test. The mechanical properties were examined at different ages of concrete by subjecting it to four different curing conditions such as water curing, admixture curing, membrane curing and air curing. M30 grade control concrete was compared with the test results. Totally 7 mix proportions by varying nano silica volume were casted. In total 50 cubes (150mm x 150mm x 150mm), 25 prisms (150mm x 150mm x 700mm) were casted to perform the experimental study. Polyethylene glycol 400 (PEG 400) was used an internal curing admixture. Sulpho-naphthalene formaldehyde (SNF) admixture was added by 0.85% weight of cement to enhance the workability of the mix. The results proved the performance of concrete was improved when cement was replaced by 2% of NS and water curing gives the best results in all the mechanical tests performed. Addition of NS beyond 2% weight of cement reduces the fresh and harden properties due to its high Specific Surface Area (SSA). The decrease in porosity was noted with NS addition, hence water curing was best suited curing technique for Nano-concrete.

Sustainable Concrete in the Construction Industry of Kurdistan-Iraq through Self-Curing

The improper curing of concrete can seriously affect its hardened properties. However, a large quantity of water is required to cure concrete after casting. Water is a valuable resource and its availability is posing a particular challenge in the Middle East including the Kurdistan region of Iraq. Self-curing concrete may be considered a novel curing method in that the water inside the concrete mix is retained so that hydration can continue without the supply of additional water after casting. Therefore, the aim of this study was to include a self-curing agent, named Polyethylene glycol-400 (PEG-400), as one of the concrete mix constituents in order to save water that is normally required after casting. Six concrete mixes were cast with a constant W/C ratio of 0.5; two of them were ordinary concrete mixes whereas the other mixes contained 0.5%, 1%, 1.5%, and 2% of PEG-400 by weight of cement. All concrete ingredients, except the PEG-400, were provided locally. Three different curing regimes were employed: air curing under ambient laboratory conditions, water curing, and self-curing using different dosages of PEG-400. Testing included compressive strength, ultrasonic pulse velocity (UPV), and water absorption. The results showed that 1% of PEG-400 is the optimum dosage to be used for self-cured concrete.

Pengaruh Penggunaan Tanah Laterit dan Kapur Padam Terhadap Kuat Tekan Mortar Geopolymer

In numerous locations of Indonesia, such as Papua, Sulawesi, and Kalimantan, there is an abundance of laterite soils, hence they have significant potential as construction materials. Geopolymer concrete and mortar have the potential to minimize the usage of Portland cement because their mechanical qualities are nearly identical to those of Portland cement-based concrete, which needs a considerable deal of energy to produce. This study examines the employment of fly ash and alkaline activators, specifically NaOH and Na2SiO3, as materials to bind lateritic soil by adding slaked lime in order to make concrete and geopolymer mortar with reduced oven use. The ratios of lateritic soil to quenched lime were 95%:5%,and 90%:10%, respectively. Flow tests conducted on fresh geopolymer mortar revealed that all ingredients were able to bond effectively and that no segregation occurred. The specimens were treated or dried in the laboratory without immersion for 3, 7, and 28 days (Laboratory Air Curing). The compressive strength test was analyzed in order to assess the geopolymer mortar's behavior. The test findings revealed that the compressive strength increased from 3 days to 7 days and 28 days. The test findings indicate that the compressive strength obtained at a ratio of 90% lateritic soil to 10% slaked lime is greater than the compressive strength obtained at a ratio of 95% lateritic soil to 5% slaked lime.

Influence of different curing methods on the compressive strength of ultra-high-performance concrete: A comprehensive review

Ultra-high-performance concrete (UHPC) is a distinguishing material used in new construction and conjunction with conventional concrete. However, some issues limit the wider application of UHPC, such as high autogenous shrinkage, low workability for large-volume production, high cost, and unpredictable peak curing method. This comprehensive study aims to clarify the different effects of curing methods on the strength development of normal concrete and UHPC. The present article reviews studies that used microwave curing, autoclave curing, carbon curing, steam curing, electric curing, ambient and air curing and water to determine their effect on compressive strength. All the curing methods achieved satisfactory values of compressive strength. However, it is not practical to specify the peak curing regimes for concrete or UHPC since the best results need critical monitoring of curing parameters. The time when the samples are demolded and subjected to hydrothermal and thermal treatments varies in the literature since it depends on the binder setting time. That time should be carefully selected to avoid adverse effects and to maximise output. A combination of these curing regimes could be used together or with pressure or heat to further improve the compressive strength. In addition to the type of materials used, the curing temperature and duration significantly affect the overall performance of concrete. This review is expected to guide future research and provide an overview of the research field.

Preparation and properties of nano-carbon black modified ultra-high-performance concrete

Ultra-high-performance concrete (UHPC) having ultra-high strength and excellent durability holds tremendous application potential in civil engineering. However, UHPC generally requires high temperature and steam curing, which not only increases the cost of UHPC, but also consumes a lot of energy. This paper presents a parametric experimental study to ascertain the basic mix proportion of UHPC cured in normal condition (wet curing and then air curing) by optimizing the gradation of sand, water-binder ratio, vibrating method, steel fiber and superplasticizer content. Afterward, nano carbon black (NCB) was used to improve the properties of this designed UHPC, and the microstructure was characterized by using mercury intrusion porosimetry (MIP). According to the test results, silica sand had the maximum packing density when mixed with 56 portions of 26–40 mesh sand, 104 portions of 40–70 mesh sand and 40 portions of 70–110 mesh sand. In addition, by using silica sand with maximum packing density, 0.18 of water/binder ratio, 1.2 of cement-sand ratio, 1.6 vol% of steel fiber and 1.0 wt% of superplasticizer, concrete had the 28-days compressive and flexural strengths respectively larger than 120 MPa and 25 MPa just after 7-days wet curing and then 21-days air curing, which meets the requirements of UHPC according to GB/T 31387–2015 (Chinese Standard). Moreover, the test results shows that the adding of 0.01%− 0.5% of NCB increased the 28-days compressive and flexural strengths of UHPC by 8.3–18.1% and 13.3–23.1%, respectively. The workability, water absorption, and drying shrinkage of UHPC were significantly improved by incorporating proper NCB content. MIP test results showed that the addition of NCB was capable of refining the pore size distribution and decreasing the porosity of UHPC.