Standard Curing Research Articles

Obsidiyen Tozu Katkılı Kendiliğinden Yerleşen Betonun Taze Beton ve Mekanik Özelliklerinin İncelenmesi

Self-compacting concrete (SCC) is a special type of concrete with high workability. This type of concrete is preferred and used as innovative concrete because it does not require vibration, has high fluidity, can be applied quickly and requires minimum workmanship. The high workability of self-compacting concrete depends on the type and amount of various chemical and mineral admixtures in its content. In this study, self-compacting concrete groups were produced by using obsidian powder, which is a rock of volcanic origin, at 15, 20 and 25% ratios instead of cement. In these groups; flow-table, V-Funnel flow, L-box, U-box fresh concrete tests and compressive strength tests were carried out after 7 and 28-days of standard water curing. When the test results are examined; it was determined that obsidian powder improved the self-compacting fresh concrete properties. In addition, it has been determined that the concrete mixtures produced using obsidian can have high compressive strength.

Permeability evolution and pore characteristics of reactive powder concrete of drilling shaft with initial salt erosion damage

The aim of this study was to investigate the relationship between permeability properties and pore characteristics of reactive powder concrete (RPC) of drilling shaft under the coupling effect of high-salinity underground water pressure and surrounding rock pressure. Stress–seepage coupling tests were performed on the RPC specimens with standard curing and autoclave curing (prepared using the same mix ratio) after composite salt damage erosion. The characteristics of initial absolute permeability and permeability evolution of RPC in the entire process of volume deformation were analyzed accordingly. Then, computed tomography and AVIZO software were used to construct a three-dimensional meso-equivalent pore network model of RPC. The model was used to analyze the spatial pore structure characteristics of both RPC specimen groups. The results showed that during volume deformation and failure, the permeability of RPC exhibited three stages along with the volume strain: obviously decreasing, sharply rising, and tending to be stable. The larger porosity and more seepage channels in the RPC matrix increased its permeability. Additionally, the pore structure obtained by three-dimensional reconstruction simulation showed that the pore throat area of the RPC specimens with standard curing and autoclave curing ranged from 0 to 11.40 mm2 and 0 to 1.35 mm2, respectively. The size distribution range of their pore throat was 1–8 mm and 1–4 mm, respectively. The research results can accelerate the application of RPC in building drilling shaft structures.

Early strength development of mortar with addition of calcium formate and electric field curing in cold climates

The rapid development of early strength of concrete in cold regions is the primary measure to ensure its resistance to frost damage. In this context, this paper incorporates 2 wt% calcium formate into a mortar and electrically cures it by passing an alternating current (AC) at a temperature of −10°C. During testing, a temperature probe monitors the real-time changes in the internal temperature of the mortar under different energisation parameters. The strength of the mortar energised for 1 day is analysed under different energisation parameters. Then, the mortar specimens are moved to a standard curing box to be cured for 3 and 7 days. X-ray diffraction (XRD), TG/DTG (thermogravimetry/derivative thermogravimetry), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) characterise the hydration products, microstructure and pore structure of the electrically cured mortar specimens. The results show that the initial resistance of the mortar specimen with calcium formate is 25% of that of the mortar without calcium formate. The 3- and 7-day strengths of the calcium formate mortar increase by 59 and 29%, respectively, compared with the mortar without calcium formate under the same energisation parameters. The combined effect of adding calcium formate and applying electrical curing densifies the pore structure of the electrically cured mortar.

Application of Steel-Fiber-Reinforced Self-Stressing Concrete in Prefabricated Pavement Joints

Prefabricated pavement, with its advantages of a high paving speed, low material consumption, low carbon emissions, high strength, and easy construction, has gradually been used to address issues associated with traditional cement pavement construction. However, even under the long-term combined effects of vehicle loads and environmental loads, the joints between pavement slabs remain prone to various problems. This paper proposes the use of steel-fiber-reinforced self-stressing concrete (SFRSSC) with a certain level of self-stress for joint pouring and connection to control the development of cracks in the joints and achieve seamless integration between the slabs. Additionally, the self-stress generated by SFRSSC is utilized to enhance the continuity of the prestressed design in precast slabs, thereby extending their service life. Through laboratory experiments and field tests, the self-stress magnitude, mechanical strength, and long-term applicability of SFRSSC were studied. The results indicate that SFRSSC can achieve self-stress levels of over 7 MPa under standard curing conditions, but the values decrease significantly when removed from the standard curing environment. SFRSSC exhibits a compressive strength of over 60 MPa and a flexural strength of over 9 MPa, both of which exceed the requirements of the relevant standards, making it suitable for use as a pavement joint material. During long-term monitoring in the field, SFRSSC demonstrates favorable expansion effects and high stability. The longitudinal expansion remains stable at 100 με, while the transverse expansion exhibits minor shrinkage, maintained at around 25.2 με. Therefore, the application of SFRSSC in assembly-type prestressed pavement joints shows high applicability.

Effect of recycled asphalt waste on mechanical properties of alkali-activated mortars

In the next century, negative effects, such as an increase in temperature level, rise in sea level and decrease in forests and agricultural areas, are expected as a result of the harmful effects of global warming. The construction industry is among the main actors of global warming. Cement, the most used building material of the construction industry, is responsible for approximately 8% of CO2 emissions worldwide. Reducing the amount of cement production and using alternative materials and wastes can contribute to reducing CO2 emissions in the production of building materials. In this study, Alkali-Activated Mortar (AAM) mixtures which contain Ground Granulated Blast Furnace Slag (GGBFS) and Fly Ash (FA) were prepared. Recycled Asphalt Waste (RAW) is reduced to 0–4 mm size in order to use as fine aggregate in AAM mixes. Three different activation temperatures (40 °C, 80 °C and 120 °C) were applied for 18 h in order to examine the effect of activation temperature on the prepared AAM samples. After the application of activation temperature, the samples were kept in the standard curing pool for 7 and 28 days. After curing, physical and mechanical experiments were carried out on AAM samples. Water absorption and porosity, compressive strength and electrical resistivity tests were performed on the hardened samples. In addition, the acid effect on the samples was investigated comparatively with the changes in mechanical and physical properties. As a result, the study, in which high-strength mortar mixtures were obtained, shows promising results in terms of sustainable environmentalism. The compressive strength value of 45.74 MPa was found in the mortar mixtures produced using RAW. In addition, it was concluded that the optimum activation temperature is an important parameter of compressive strength and acid resistance.

Study on the mechanical properties and pore structure of granulated blast furnace slag self-compacting concrete based on grey correlation theory

ABSTRACT Variations in the mechanical properties and pore structure of granulated blast furnace slag self-compacting concrete were studied. The grey correlation theory established the relationship between mechanical properties and pore structure. The test results show that with the continuous improvement of age, the mechanical properties decreased with the increase of sand replacement rate in the early stage. In the middle and late stages, the compressive strength and splitting tensile strength of granulated blast furnace slag self-compacting concrete are higher than those of ordinary self-compacting concrete, while the elastic modulus continues to decrease with increasing slag content. After standard curing, the change in the pore structure parameters of ordinary self-compacting concrete is relatively stable. The pore structure parameters of granulated blast furnace slag self-compacting concrete change significantly. Because granulated blast furnace slag has a certain hydraulicity, the strength and strength growth rate of granulated blast furnace slag self-compacting concrete are higher than those of ordinary self-compacting concrete, and the corresponding pore structure parameters change. Through grey correlation analysis, the specific surface area and average chord length structure of granulated blast furnace slag self-compacting concrete are essential factors affecting its mechanical properties.

Experimental Study of Sulfate Erosion Resistance of Cementitious Sand with Waste Glass Powder

In order to save natural resources and protect the natural environment, the relevant performance of waste glass powder as a building material must be enhanced. In general, volcanic ash activity is enhanced through grinding the glass powder particles to a specific degree of fineness, thereby improving the overall strength of cementitious sand. Our current need is to study the effects of replacing standard sand with glass powder of varying particle size and dosage range on its resistance to sulfate erosion as well as the corresponding mechanisms. To further examine the durability properties of glass powder cementitious sand, this study uses glass powder of 100–200 mesh and 200–500 mesh to create cementitious sand samples, replacing 10% and 15% of standard sand with equal volume. After curing for 28 days in a standard curing room, the samples are submerged in tap water and a 5% concentration of sodium sulfate solution for 30, 60, 90, 120, and 150 days. Subsequently, the mass loss rate, flexural strength, and compressive strength are measured to reflect the sulfate erosion resistance of the cementitious sand samples containing glass powder. The findings indicate that the flexural and compressive strengths of cementitious sand with waste glass powder experience a swift decline in strength during the pre-erosion stage and a slow decline or even an increase in strength during the post-erosion stage as erosion age progresses. As the glass powder dosage increases, there is a noticeable decrease in the flexural and compressive strengths, in which the doping of 200–500 mesh doped with 15% of glass powder has the worst effect on the resistance to sulfate erosion. As the particle size increases, both flexural and compressive strengths significantly improve, suggesting that sulfate erosion properties are gradually enhanced. The primary reason for this phenomenon is that when glass powder substitutes fine aggregate, the activity develops more slowly in the initial stage, primarily filling the pores and cracks. However, the activity increases rapidly later, more fully integrating with the cement mortar in sodium hydroxide’s hydration product to create dense hydrated calcium silicate crystals. This enhances the overall strength of the sample, filling the pore structure within the system, and is more conducive to resisting the erosion effect of sulfate ions on the sample.

Unleashing the potential of bio-based concrete: Investigating its long-term mechanical strength and drying shrinkage in real climatic environments

Natural climatic conditions have significant negative impacts on the long-term mechanical properties and dimensional stability of bio-based concrete considering the high water absorption of bio-aggregates and corresponding biodegradations. In this study, the effects of three hydrophobic treatments (integral mixing, aggregate coating, concrete coating) on the physical properties, mechanical strengths, and drying shrinkage characteristics of bio-based peach kernel shell concrete in real climatic natural environments are investigated. Results show that bio-based peach kernel shell concrete has lower mechanical strength in outdoor climatic conditions than in indoor standard curing conditions. The swelling and shrinkage process causes the visible microcrack and debonding between bio-based materials and mortar interface. The drying shrinkage of bio-based peach kernel shell concrete in outdoor conditions is highly dependent on real climatic environments, including temperature, humidity and rainfall. The hydrophobic surface-coated concrete exhibits excellent resistance to real climatic environments, as well as good mechanical strength and dimensional stability, with 15.7% less drying shrinkage in 18 months, compared to reference concrete. Moreover, cellulose and hemicellulose of heat-treated bio-aggregates do not degrade over time in outdoor conditions due to the enhanced biodegradation resistance. The hydrophobic surface coating treatment is recommended for enhancing the service life of bio-based peach kernel shell concrete in real climatic environments.

Comparison of nano-silica-modified manufactured-sand concrete under steam curing and standard curing

Comparison of nano-silica-modified manufactured-sand concrete under steam curing and standard curing

Relationship between fractal characteristics of pore-structure and thermal properties of FA-based AAM under different curing conditions

The microstructure of hardened alkali-activated materials (AAM) plays an essential role in determining the mechanical properties at elevated temperatures, particularly the pore structure. Mercury Intrusion Porosimeter (MIP) was employed to study the fractal characteristics of the pore structure of samples under standard and sealed curing conditions, which includes pore size distribution, shape, surface area, and tortuosity of AAM pastes after exposure to high temperatures. Additionally, the compressive strength of AAMs at elevated temperatures was determined. Comparing the samples under standard curing conditions, sealed curing conditions significantly improved the 28-day compressive strength (43.6 MPa) and residual compressive strength (achieving 60.2% of the 28-day strength) when exposed to 1000 °C. Based on research, the fractal characteristics of pore structures have a significant effect on the thermal properties of samples at high temperatures. Differences in thermal properties may be attributable to resistance caused by pore structures with heterogeneity and complexity, as well as the shape of the pores, which have small pore throats and large pore capacities. Under standard curing conditions, the samples exhibited a pore structure characterized by a reduced neck diameter, larger cavity size, a coarser pore surface, and decreased connectivity. As a result, the 28-day samples under standard curing conditions experienced significantly elevated pore pressure.

Sustainable ultra-high performance concrete with incorporating mineral admixtures: Workability, mechanical property and durability under freeze-thaw cycles

This paper evaluates the influence of mineral admixtures partially replacing cement, sea sand replacing quartz, sea water replacing fresh water on ultra-high performance concrete (UHPC). The fluidity and mechanical properties were studied. Besides, the impermeability, chloride resistance and freeze-thaw resistance were investigated. Failure modes, scanning electron microscope (SEM) analysis, mass loss, relative dynamic modulus of elasticity and mechanical properties of UHPCs after freeze-thaw cycles were conducted. The results showed the fluidity of UHPC paste gradually increases with the improvement of water-binder ratio. It is recommended that the water-binder ratio of UHPC be set at 0.19. The fluidity also increases with the improvement of the content of slag, fly ash and water reducer, but decreases with the improvement of silica fume content. The flexural and compressive strengths of UHPC enhance with the improvement of the content of silica fume, but reduce with the improvement of the content of fly ash and slag. The UHPCs made of quartz sand, river sand and sea sand, all, achieve a high strength. UHPCs prepared at standard curing conditions, with or without steel fibers, mixed by artificial seawater and made of sea sand, exhibited excellent impermeability and chloride resistance. The frost resistant grade of all UHPC specimens prepared by standard curing are greater than F500 exhibiting excellent freeze-thaw resistance and sustainability.

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.

Coordination Compound (2,3,5-Triphenyltetrazolium)2[CuBr4] as Catalyst for the Curing Process of Epoxy Vinyl Ester Binders.

This article presents a study on the synthesis and catalytic properties of copper complex (TPhTz)2[CuBr4] (here TPhTz is 2,3,5-triphenyltetrazolium). The obtained complex was characterized by various spectroscopic methods. The catalytic properties of the complex were evaluated in the curing of an epoxy vinyl ester system and their effectiveness was compared with that of cobalt octoate (its synonyms are known as Co(Oct)2, cobalt(II) 2-ethylhexanoate, cobalt isocaprylate, etc.). The catalyst was added at an amount of 2 w.%. The results showed that a 8 w.% solution of the complex provides catalytic properties with an activation energy of 54.7 kJ/mol, which is 25.2 kJ/mol higher than a standard curing system with Co(Oct)2. Thus, the solution of (TPhTz)2[CuBr4] in THF/DMSO accelerates the initiator decay process at room temperature, but for a longer time. The authors suggest that the curing mechanism may be accelerated by the appearance of (TPhTz)2[CuIBr3] and free bromine in the system. A strength test of fiberglass-reinforced plastic revealed that the addition of this complex did not lead to a decrease in flexural strength and hardness. Thus, use of the complex allowed for the production of polymer composite products using vacuum-assisted resin transfer molding where an extended injection time was needed.

Engineering Properties of Novel Vertical Cutoff Wall Backfills Composed of Alkali-Activated Slag, Polymer-Amended Bentonite and Sand.

The workability, hydraulic conductivity, and mechanical properties are essential to contaminant containment performance of cementitious backfills in vertical cutoff walls at contaminated sites. This study aims to investigate the engineering properties of a novel vertical cutoff wall backfill composed of reactive magnesia (MgO)-activated ground granulated blast furnace slag (GGBS), sodium-activated calcium bentonite amended with polyacrylamide cellulose (PAC), and clean sand (referred to as MSBS-PAC). Backfills composed of MgO-activated GGBS, sodium-activated calcium bentonite, and clean sand (referred to as MSBS) were also tested for comparison purposes. A series of tests were conducted which included slump test, flexible-wall hydraulic conductivity test, and unconfined compression test. The pore size distributions of two types of backfills were investigated via the nuclear magnetic resonance (NMR) technique. The results showed the moisture content corresponding to the target slump height was higher for MSBS-PAC backfill than that for MSBS backfill. The MSBS-PAC backfill possessed lower pH, dry density, and higher void ratio at different standard curing times as compared to MSBS backfill. The unconfined compressive strength and strain at failure of the MSBS-PAC backfill were noticeable lower than those of the MSBS backfill. In contrast, the hydraulic conductivity of MSBS-PAC backfill was approximately one order of magnitude lower than that of the MSBS backfill, which was less than 10-9 m/s after 28-day and 90-day curing. Lower hydraulic conductivity of MSBS-PAC backfill was attributed to the improvement of pore structure and pore fluid environment by PAC amendment.

Performance and microscopic study of various mineral admixtures on reactive powder concrete

A ternary admixture system of industrial waste (silica fume (SF), slag powder (SL), and fly ash (FA)) was used to replace quartz powder and reduce the cement content to prepare green, low-carbon and high-performance cement-based materials. The mechanical properties of RPC under natural watering curing (NWC), standard curing (TC), and mixed curing (MC) conditions were studied, and the influencing mechanism was analyzed and explored from a microscopic perspective. The results show that the MC curing system promotes the early hydration of cement and improves the compactness of the matrix. However, the strength in the later stage was affected by temperature internal force, and the compressive and splitting tensile strength in the later stage increased by −0.1% and −36.27%, respectively. The 28 day compressive strength of RPC under TC and NSC conditions increased by 10.30% and 11.78% compared to 7 days, while the splitting tensile strength increased by 17.42% and 14.10%, and the difference between RPC and MC strength gradually decreased.

Frost resistance and life prediction of equal strength concrete under negative temperature curing

The compressive strength of concrete cured at −3 °C increases with age and can reach an equal strength to that of concrete cured at 28d of standard curing. However, the frost resistance of concrete with equal strength remains unclear. The mass loss, relative dynamic elastic modulus, peak stress, and peak strain of concrete are selected for evaluating the frost resistance of equal strength concrete. The results show that the negative temperature curing reduces the frost resistance of equal strength concrete, and the frost resistance of concrete decreases with the water-binder ratio. The optimal initial air content of equal strength concrete for frost resistance is between 4% and 5%. The calculation models of the relative peak stress and relative peak strain of equal strength concrete are established considering the initial air content and freeze–thaw cycle times. Based on the rapid coefficient method, the relationship between laboratory accelerated testing and the on-site service life of concrete is established, taking the relative dynamic elastic modulus reduced to 60% as the criterion of freeze–thaw failure, the life prediction of equal strength concrete is carried out. The equal strength concrete cured at −3 °C cannot achieve equal frost resistance and service life.

Contribution to the Concrete Structure Project Executed with Rolled Pebbles in the City of Manaus – Usual Procedures and Recommended Standards

Initially, the aggregates used in concrete construction available in the building materials market in the city of Manaus were assessed. Samples were collected from the North, South, East, and West zones to determine their quality indices and physical properties, with the aim of producing concrete mix designs using regional materials. Subsequently, prototypes of slabs and beams were constructed to obtain concrete cores for evaluating their compressive strengths. These elements were exposed to outdoor environmental conditions, including rain, sunlight, and wind. One group was also subjected to wetting and drying cycles at the beginning and end of each day. Additionally, cylindrical specimens were cast for axial compression tests. During the concrete curing phase, these specimens were identified and divided into two groups exposed to different conditions: immersion in a saturated calcium hydroxide solution, outdoor exposure, outdoor exposure in a covered environment, and outdoor exposure subjected to wetting and drying cycles. The experiments were conducted over the course of a year to assess the influence of environmental conditions, including relative humidity and temperature, on concrete strength. The results revealed that environmental conditions, during the period from July to November, in conjunction with the standard curing method adopted in the city of Manaus (wetting the surfaces at the beginning and end of each day), affect the concrete’s strength gain, resulting in a final value lower than expected. This not only reduces the load-bearing capacity of the structure but also increases concrete porosity and reduces its modulus of elasticity. Therefore, when designing and constructing concrete structures in Manaus, the region’s specific characteristics must be considered. These considerations should encompass aggregate types, environmental conditions, and the local curing practices.

Effect of Preparation Technology on Properties of Cellular Concrete

The volume method is used to calculate the mix ratio of porous concrete. According to the special structure of porous concrete, the influence of different mixing technology, forming technology and curing technology on the performance of concrete is analyzed. The test results show that the coating method is more suitable for mixing porous concrete than the single feed method. Appropriate vibration and pressure can increase the strength of porous concrete. Under the condition of suitable temperature, the moisture curing effect of covering geotextile is roughly the same as that of standard curing, which has a practical reference for the preparation and site construction of porous concrete.

Ispitivanje primjene otpadnih mineralnih dodataka u betonu ultravisokih svojstava

This study examined the effects of various waste materials on the properties of ultra-high-performance concrete (UHPC), along with their designs and ideal mix ratios. Several UHPC mixtures have been developed using the Taguchi L16 method, which generally forms part of the experimental programs for evaluating the properties of UHPCs. Furthermore, the proportions of the component materials were chosen based on approximate ranges found in literature. The samples were cured under two different regimes: standard immersion water curing (SC) and hot water immersion curing (HC). The properties of both hardened and fresh concretes were assessed. A flow test was conducted on the fresh concrete to determine the workability, and a standard test was conducted to assess the density. To investigate a hardened concrete sample, the compressive and flexural strengths were examined and density, absorption, and void tests were conducted. The results obtained from the Taguchi approach for the compressive strength at 28 days were found to be 20 % for SF, 0 % for FA, and 0 % for GBFS; the flexural strength was 10 % for SF, 0 % for FA, and 0 % for GBFS. The compressive strength was 147.07 MPa with SC and 150.13 MPa with HC and flexural strength was 26.88 MPa with SC and 27.31 MPa with HC (as conducted at 28 days in a mixture of 10 % SF and 10 % GBFS).

EFFECT OF SEA SAND WITH DIFFERENT CHLORIDE ION CONTENTS ON THE PROPERTIES OF CONCRETE

This article presents the results of a study that evaluated the effects of using sea sand with varying contents of chloride ions on the properties of concrete, including physical and mechanical properties as well as durability. The study was carried out on the sea sand samples with different chloride ion contents, including as-received sea sand samples with a chloride ion content of approximately 0.15%, two washed (desalted) sea sand samples with chloride ion content of 0.024% and 0.05%, and sea sand samples added with chloride salt (0.375%), which were then compared with river sand samples. The sand samples had approximately the same fineness modulus ranging from 2.3-2.5. The research results indicated that compared with washed sea sand and river sand, concrete mixes using sea sand with high chloride ion content increased the mixing water and reduced the slump retainability of the fresh concrete. Furthermore, early compressive strength (7 days) increased but late age strength (91 and 365 days) decreased in both standard curing and wet-dry circle curing cases. Additionally, the impermeability (water and chloride ion) and the ability to protect the reinforcement from corrosion in concrete were reduced when using sea sand with high chloride ion content compared to washed sea sand and river sand.