Early Strength Of Concrete Research Articles

Enhancing Concrete with Ultrafine Fly Ash: Mechanical Strength and Frost Resistance

Fly ash, a byproduct collected from the flue gas of coal combustion, serves as an effective additive in concrete. It offers environmental benefits by converting waste into a valuable resource, thus promoting energy conservation, emission reduction, and waste utilization. Additionally, fly ash enhances the mechanical properties and frost durability of concrete. Commonly used as a partial substitute for cement, it helps conserve resources. However, its use may compromise early strength and durability, which limits its applications. The transformation of raw fly ash into ultrafine fly ash through mechanical grinding increases its fineness and specific surface area, thereby boosting its reactivity and micro-aggregate effects. This process produces denser C-S-H gel and optimizes the concrete microstructure. Research shows that although ultrafine fly ash may slightly reduce early concrete strength, it significantly enhances long-term strength, with a 10% substitution improving early compressive strength by 20.2% and later strength by 13.7%. However, excessive fly ash content can reduce frost resistance, with an optimal substitution level at 25% significantly enhancing this property compared to standard concrete. Blending ultrafine fly ash with other mineral admixtures further boosts mechanical properties and frost durability. Challenges include increased processing costs and early strength deficiencies, along with the necessity to control heavy metal content for environmental and health safety. Future research should aim to optimize fly ash particle distribution and reactivity, develop cost-effective production methods, and blend fly ash with other minerals to improve concrete’s mechanical and frost resistance properties, thus expanding its potential applications.

The Influence Of Adding Superplasticizer With Time Interval And Variation Of Water Reduction On The Early Strength And Workability Of Concrete

Acceleration of early strength of concrete can be obtained by reducing water in the concrete mixture followed by addition of superplasticizer. The application of the addition of superplasticiser to water-reduced concrete mixtures requires innovation in providing a time lag to produce good workability. This study analyzes the effect of giving a time delay when adding superplasticizer followed by reducing water with certain variations on the workability and early strength of concrete. The results of this research are very important for the concrete industry with the purpose of shortening the removal time of formwork and optimizing the construction process. Water cement ratio is adjusted by reducing its volume by a fraction of 10% to 30%, superplasticizer 1% to the weight of cement is added in two stages, during the initial mixing and after one or two hours afterwards. 0.3% retarder was added to control homogeneity during mixing. The test results concluded that the reduction of water that provided the highest increase in concrete compressive strength at 4 days was LN25-1 of 21.94 MPa (87% of the design compressive strength) and LN20-2 of 19.12 MPa (76% of the compressive strength plan). The optimal amount of water reduction at the initial age of the concrete is 20 – 25% of the design water weight. Giving a time lag does not reduce the increase in concrete strength due to the addition of superplasticizer.

Impacts of corrosion inhibiting admixture and supplementary cementitious material on early strength concrete

This research aimed to evaluate the influence of alccofine 1203 on a mineral admixture and sodium nitrite as a corrosion inhibitor on the properties of concrete. To achieve these aims, an experimental investigation was carried out on a set of composite samples comprising five distinct concrete formulations. Five different mixes for the concrete were used as the overlay materials such as NC as a reference concrete, alccofine concrete (i.e. 25% cement replaced with alccofine), and alccofine concrete with varying dosages of sodium nitrite (i.e. 1%, 1.25%, and 1.5%). Alccofine reduced the workability and water absorption and increased the compressive strength of the concrete (5%) at curing age of 28 days. Adding sodium nitrite further reduced water absorption of the concrete and workability but compressive strength of 29.15% and 26.93% for the curing period of 3 and 7 days, respectively. The pH of the concrete powdered solution became more alkaline with the replacement of alccofine and addition of sodium nitrite. Free chloride content dropped by 48 and 66%, respectively, with the introduction of GGBS and sodium nitrite. Corrosion properties of the concrete samples were examined using open circuit potentials and linear polarization resistance of various concrete mixes after being immersed in 1 M H2SO4 and 3% NaCl environment. The findings indicated a notable improvement in the corrosion resistance, water absorption test, thermal conductivity, strength properties, and microstructural properties of concrete with the incorporation of SN in combination with alccofine. The application of the response surface method allowed for the prediction, validation, and optimization of experimental data using a regression equation.

Early Strength of Concrete by using Ground Granulated Blast Furnace Slag and Local Ordinary Portland Cement Materials

It is well known that using Ground Granulated Blast Furnace Slag (GGBFS) to replace some of the cement in concrete will cause it to take longer to reach its ideal compressive strength. However, several precast concrete manufacturing processes require high initial compressive strength values to speed up production. The impact of partially substituting GGBFS for cement on the initial strength values of concrete is investigated in this work. The 300 concrete cylinder samples were used to accomplish the study's goals. Compressive and split tensile tests determined the concrete's initial compressive strength and split tensile strength outputs. Therefore, the ideal percentage of GGBFS can replace cement by 20–30% to achieve the desired early compressive strength of 16 MPa in 16 hours by setting the proper water-cement (w/c) ratio at about 0.25. Because a low w/c ratio leads to low workability, some additives, such as silica fume or superplasticizer, can be employed to further increase the workability and performance of concrete.

Effect of Limestone Powder Mixing Methods on the Performance of Mass Concrete.

Using limestone powder (LP), the by-product of manufactured sand, to replace part of fly ash (FA) or manufactured sand could not only turn waste into treasure and decrease the price of concrete, but could also enhance the performance of concrete and reduce environmental pollution. However, the impact of various LP incorporation methods on the performance of mass concrete was inconsistent. In this paper, the effects of LP on the workability, compressive strength, constrained expansion rate, hydration temperature and impermeability of mass concrete were studied by replacing FA or manufactured sand alone and replacing FA and manufactured sand simultaneously. The results showed that the impact of LP on the performance of mass concrete was equal when it replaced FA alone and FA and manufactured sand at the same time. When the replacement amount was 20%, the workability, expansibility and early strength of concrete were improved, but the later strength and impermeability were slightly reduced. The workability, compressive strength, expansibility and impermeability of mass concrete were improved when manufactured sand was replaced alone, and the optimal dosage was 10%. The LP, moreover, reduced the hydration temperature peak of concrete in three kinds of mixing methods, but the temperature peak appeared earlier. At lower dosages, LP optimized pore structure and promoted the early hydration of cement through filler effects and nucleation effects. When LP replaced manufactured sand, the microstructure of concrete was more dense, so the replacement of manufactured sand had a better effect on the improvement of concrete properties. A reference value for the use of LP in mass concrete is provided in this study.

Effect of Accelerators on High Early Strength Concrete (HESC) Using High Volume Fly Ash

Applying large quantities of fly ash for the production of High Early Strength Concrete (HESC) is a challenge for researchers in the utilization of quality, inexpensive, and environmentally friendly materials. A high volume of fly ash in concrete, however, reduces the initial compressive strength of the concrete. For this reason, it is necessary to use admixture additives in the concrete mixture to get the expected performance. This research seeks to identify the optimal HESC mix design using fly ash 50% of the total cementitious by adding a superplasticizer and accelerator to obtain a high initial compressive strength. Three variations of HESC, namely HESC-12, HESC-14, and HESC-16, were made using a superplasticizer and accelerator with different doses. Each variation uses 12 liters of superplasticizer and different accelerator volumes: 12 liters, 14 liters, and 16 liters. Specimen testing was carried out on fresh and hard concrete. Fresh concrete was subjected to a slump test, whereas hard concrete was subjected to compressive tests at 18 hours, 24 hours, 3 days, and 28 days of age. The average slump flow values for HESC-12, HESC-14, and HESC-16 (cm) were 78, 79.5, and 80, respectively, demonstrating that all HESC samples are classified as self-compacting concrete (SCC). According to the results of density tests conducted on all specimens ranging from 2461 to 2538 kg/m3, all specimens are included in the category of normal-weight concrete. Within the range of 29.8 to 35.3 MPa for the initial compressive strength of HESC at 24 hours of age, it can be concluded that all HESC specimens fulfill the criteria for high early-strength concrete. The addition of the right type and dosage of chemical admixture is a solution to overcome the weakness of applying fly ash in high-early-strength concrete.

Study on the Influence of Shrinkage-Reducing Materials on the Volume Stability of Shotcrete with a Fluorine-Containing Alkali-Free Accelerator.

In contrast to ordinary concrete, shotcrete exhibits greater shrinkage deformation. The utilization of an aluminum fluoride alkali-free accelerator (AF) is prevalent in tunnel engineering, attributed to its economical nature and fast setting and hardening. Currently, there is a dearth of research on the volume stability of aluminum fluoride accelerators, and no relevant studies have been conducted on the application of shrinkage-reducing materials in shotcrete using an aluminum fluoride accelerator. With the use of an aluminum fluoride accelerator, the early strength of shotcrete is reduced, and the addition of a shrinkage-reducing agent (SRA) and super-absorbent polymer (SAP) can also lead to a further reduction in the early strength of concrete. Therefore, this study aims to investigate the influence of these two shrinkage-reducing materials (SRA and SAP) on the workability and mechanical properties of shotcrete. The primary focus of this research is to determine the better compensation effect of the two shrinkage-reducing materials. To accomplish this, the study focuses on assessing the setting time, compressive strength, and volume stability of shotcrete that has been mixed with an aluminum fluoride accelerator using SRA and SAP. Additionally, we also aim to explore the hydration and shrinkage compensation mechanism of these shrinkage-reducing materials on shotcrete by conducting a microscopic test analysis.

Effects of nano-silica modification on early age hydration process in winter construction of tunnel engineering

Fast hardening and high early strength are crucial factors for concrete used in tunnel construction in cold regions. The incorporation of nano-silicate has been found to be an effective method for improving the properties of cement-based materials at an early age. Thus, the objective of this paper is to investigate the nano-modification effects of different nano-silica contents on the hydration process, mechanical properties, and hydration products of cement cured in a low-temperature environment. The effects of various nano-silica concentrations, including 1%, 2%, 3%, and a high dose of 6%, on the properties of the concrete were investigated. According to the test results, the optimal quantity of nano-silica plays a crucial role in determining the properties of concrete. The effects of nano-silica on the hydration of C3A were found to dominate the cement hydration process at an early age. The incorporation of nano-silica led to a significant improvement in the dissolution rate of anhydrite and the reaction rate of the C3A renewal, which may be responsible for the gain in early strength of concrete. However, an excessive amount of nano-silica could negatively affect the hydration process of the alite and C3A, as evidenced by the total heat generated during the silica and aluminate reactions. The XRD patterns further confirmed these results.

Early age dynamic mechanical properties of basalt fiber reinforced early strength concrete

AbstractThe dynamic compression test was carried out on basalt fiber reinforced early strength concrete (BFRESC) with ages of 4–24 h by the split Hopkinson pressure bar (SHPB) test system. The effects of curing age and basalt fiber content on dynamic mechanical properties of ESC was analyzed. The result shows that the dynamic compressive strength and specific energy absorption of BFRESC at early ages increase continuously with the increase of fiber content. The dynamic compressive strength of concrete at the early ages increases exponentially with the strain rate. With the increase of curing age, the strain rate sensitivity of dynamic compressive strength of concrete increases gradually, and the strain rate sensitivity of dynamic compressive strength of BFRESC with fiber content of 0.1% is the strongest. The specific energy absorption of concrete at early ages increases linearly with the strain rate. With the increase of curing age, the strain rate sensitivity of specific energy absorption of concrete increases gradually, and basalt fiber can enhance the strain rate sensitivity of specific energy absorption of concrete. Based on the comparison with the formula for dynamic increase factor (DIF) calculation provided by Comite Euro‐International du Beton (CEB), etc., a model of DIF based on the increase of curing age is proposed.

Early Mechanical and Microstructure Evolution Characteristics of Concrete in Steam Curing Condition

In order to study the effect of steam curing on early mechanical properties of concrete, the strength, dynamic elastic modulus, and microstructure characteristics of concrete under different curing methods were tested. The results show that the early strength growth rate of steam curing concrete is obviously higher than that of standard curing. The strength development of concrete during steam curing can be divided into three stages. Stage I and stage II (0 h-30 h) are critical periods for concrete strength growth. The dynamic elastic modulus of steam-curing concrete is mainly formed in the early stage and shows a linear rapid growth characteristic. The growth rate of the dynamic elastic modulus of concrete under standard curing condition is relatively slow, but in the later curing period (30 h-48 h), the growth rate of dynamic elastic modulus of concrete is significantly higher than that of steam curing concrete. Steam curing can accelerate the production of cement hydration products which rapidly increases the early strength of concrete. Under the standard curing condition, the hydration product structure of concrete is more compact, which is conducive to the growth of dynamic elastic modulus in a later period. This study provides a theoretical reference for the application of steam curing in engineering, which is important to ensure the production efficiency and quality of concrete in engineering.

Effects of Nanomaterials Reinforced Aggregate on Mechanical Properties and Microstructure of Recycled Brick Aggregate Concrete

In this paper, the effects of nano-SiO2 and nano-Al2O3 on the brick aggregate properties, compressive strength of brick aggregate concrete at different ages, and microstructure of brick aggregate concrete are investigated. The results show that the water absorption of recycled brick aggregate decreases with the increase of nanomaterials solution concentrations, and the crush index of recycled brick aggregate decreases. Nano-SiO2 and nano-Al2O3 improve the compressive strength of recycled brick aggregate concrete at different ages, and the effect of nanomaterials on the early strength of concrete are more obvious. With the increase of nano-solution concentration, the compressive strength of nano-SiO2 reinforced brick aggregate concrete increases first and then decreases, while that of nano-Al2O3 reinforced brick aggregate concrete increases. The internal structure of nanomaterials reinforced brick aggregate is denser, micro cracks and pores are filled with hydration products, and the interfacial transition zone is more compact.

Review on the Role of Ultra-fine Fly Ash on the Performance of Concrete

Fly ash is mainly the solid waste emitted by coal-fired fossil fuel power stations, which is collected through the flue gas emitted. At present, the comprehensive utilization of fly ash has been widely promoted and applied in actual production. The application of fly ash to concrete can not only improve the strength of concrete, but also save cement. However, its hydration rate is slow, and the incorporation of concrete will reduce the early strength of concrete. In order to improve the activity and other properties of fly ash, ultrafine fly ash with small particle size is obtained by grinding fly ash. Ultrafine fly ash has finer particle size than fly ash and larger spherical shape than original fly ash. Water demand decreases, density increases and activity increases. It can better fill the cement void, improve the internal compactness of concrete, and improve the interface structure of materials. Research has shown that adding 10% to 20% fly ash can achieve better performance than conventional concrete. For higher fly ash content, the strength decreases with the increase of fly ash content.

Study on the Influence of Early Strength Polycarboxylate Superplasticizer on Early Performance of Concrete

A series of polycarboxylate ether (PCE) based superplasticizers with early-strength functional monomers were prepared to study the influence of early-strength PCE on the hydration heat of cement, early strength properties, and setting time of concrete. It was found that PCE containing DAC and UP-152 had the most obvious improvement in the early strength performance of concrete, greatly improved the dispersibility of cement particles, accelerated the formation of C-S-H gel, enhanced the early hydration performance, and early advanced the setting time of concrete. It can also reduce the pores and gaps in the cement concrete and improve its compactness. Finally, it had the most prominent effect on the early strength of concrete.

Optimum Curing Regimes of Early Strength Concrete Inclusive of Heat Transfer and Hydration Effects

The optimum curing regime (OCR) empirically obtained from a number of small-sized specimens may be overly conservative or inaccurate due to neglecting the effects of exothermic hydration and geometries of full-sized members related to heat transfer. This study presents a theoretical model considering these effects to determine the OCRs of early strength concrete (ESC) in a Pareto set from an extensive design space. To validate the model, experiments were performed to measure the temperature histories and strength development under steam-curing conditions for a full-sized beam segment and match-cured small cylinders made of ESC. Parametric studies showed that energy savings of 7.5%, 20.4%, 42.7%, and 56.3% in steam curing could be achieved with the increase of the maximum steam temperature, sectional area, cooling period in the curing regime, and compressive strength of ESC, respectively. The most significant energy saving, 66.1%, was realized by including the favorable effects of hydration, compared with the results of OCR without hydration for the section considered in this study.

The role of ultra-fine supplementary cementitious materials in the durability and microstructure of airport pavement concrete

Conventional Supplementary cementitious materials (SCMs) are indispensable constituents of high-performance concrete, despite their potential drawback of reducing the early strength of concrete. Ultra-fine supplementary cementitious materials (USCMs) have been employed to expedite the pozzolanic reaction and refine micro-scale particle gradation in airport pavement concrete. The investigation encompassed an assessment of mechanical properties, durability, phase assemblage, pore structure, morphology, and microstructure. Results showed that the incorporation of USCMs significantly enhanced the flexural and compressive strength of concrete during the early age, exhibiting respective improvements of 25.4% and 12.8%, respectively. Moreover, the freezing-thawing resistance was enhanced by a factor of 1.6, and the chloride penetration resistance was improved approximately 4 times. These enhancements can be attributed to the heightened pozzolanic and filling effects of USCMs, which resulted in the consumption of more calcium hydroxide (CH) at 7 d and facilitated the growth of additional calcium silicate hydrate (C-S-H) gel, along with lowering hydration heat and decreasing remarkably porosity. Notably, the incorporation of USCMs led to a considerable improvement in the volume fraction of harmless pores (with pore diameter ≤ 50 nm), optimizing the pore structure of the concrete and thereby augmenting its mechanical properties and durability.

Research on Optimization Design of the Mix Proportion of Xiamen Second East Passage Tunnel

Because of the poor hydration heat and shrinkage of the tunnel constructed in sections, structural cracks are easy to occur, and the concrete mix ratio is very important. In order to achieve accurate concrete mix proportion, the paper has optimized the concrete mix proportion of Xiamen East Second Passage. The early mechanical properties and impermeability of the concrete before and after the optimization of the mix ratio were tested. The results show that the cement content in the original design mix proportion is high, the early strength of concrete is excessive, and high hydration heat and shrinkage are easy to occur during construction. The early mechanical properties and impermeability of the optimized mix proportion concrete can meet the design and construction requirements. The conclusions can provide guidance for the construction of similar projects.he construction of similar projects.

Influence of accelerating admixtures on high early strength cement performance using heat curing method

Recently, early-strength concrete has been applied widely in high-rise buildings and rigid pavement maintenance due to its advantages in time and cost reduction, and its construction efficiency. Admixtures including setting accelerators and hardening accelerators, are usually used to achieve high early-strength concrete. However, the mechanism of those admixtures at the early age of cement hydration was not clearly examined. Hence, this research investigated the influence of setting accelerators, hardening accelerators and their combinations on the hydration of cement paste using the heat curing method for the application to rigid pavement maintenance, and precast concrete. By evaluating the differences between the setting time, early compressive strength, exothermic curves, XRD patterns, and Fe-SEM images of the cement paste with and without adding Potassium bromide (KBr), Calcium formate (Ca(HCOO)2), and their combination, the results indicated that the addition of setting accelerators such as Ca(HCOO)2 had a significant effect on the setting behavior of cement paste instead of the compressive strength enhancement. Therefore, the addition of Ca(HCOO)2 also had a low effect on the mechanical strength of the paste when increasing the curing temperature. In contrast, the addition of hardening accelerators such as KBr had a greater accelerating impact on the mechanical strength of the cement paste when increasing the curing temperature. Combining a setting accelerator and a hardening accelerator could greatly improve cement paste early-age compressive strength for both normal and heat curing. Based on the XRD analysis, and the Fe-SEM results, numerous hydration products were formed in early-age cement hydration by the addition of 2.0 % KBr with 3.0 % Ca(HCOO)2, especially in 8 h of 50 °C curing temperature. Hence, this combination significantly enhanced the early mechanical strength of the cement pastes.

Performance of High Early Strength Concrete (HESC) using Different Superplasticizer

High Early Strength Concrete (HESC) is one type of high-performance concrete. HESC production requires high-quality materials and additives, namely chemical admixture type C (superplasticizer) to get high performance. This study aims to obtain a HESC mix design using a superplasticizer with the best performance. The 3 variations of HESC are made by adding a superplasticizer to a mixed concrete with the same dosage but from 3 different manufacturers, namely HESC-1, HESC-2, and HESC-3. Specimens performance consisted of tests for both fresh concrete and hardened concrete. The fresh concrete was tested by the slump, and the hardened concrete was tested by density and compressive strength tested at the age of 12 hours, 14 hours, and 3 days on cylindrical specimens measuring 100 mm x 200 mm which have been cured by water curing. Based on the test results, it was found that the average slump values in HESC-1, HESC-2, and HESC-2 were (cm): 64.0, 69.5, and 70.5. This shows that all HESC specimens are categorized as Self Compacting Concrete. According to the results of the density test on all specimens ranging from 2382 to 2436 kg/m3, all specimens are included in normal-weight concrete. With the initial compressive strength value of HESC at the age of 14 hours in the range of 21.0 to 24.9 Mpa, it can be concluded that all HESC specimens meet the requirements of High Early Strength Concrete, where HESC-3 is the best performance one.

Mechanical behavior of flowing concrete and early strength concrete with the addition of type D and F admixtures

Flowing concrete (FC) and self-compacting concrete (SCC) that are produced with admixtures can be a solution to the complexity of construction problems. Self-compacting concrete is a special type of flowing concrete, but flowing concrete is not necessarily self-compacting concrete. This paper investigates the adding type D and F admixtures with andesite stone as the potential local coarse aggregate materials which were abundantly available for flowing concrete and early strength concrete (ESC) performance. This study has two test categories: fresh concrete and hardened concrete. The fresh concrete category includes slump, slump flow, and T500 tests. Meanwhile, the hardened concrete category includes compressive, splitting tensile, and flexural strength tests. The experimental results indicated that the admixture type F dosage of 1.0%, 1.55% and 1.75% cement weight can enhance the compressive strength by 3.88%, 5.82% and 9.71% respectively. The combination of type F and D admixtures with dosage of 0.15% and 0.2% cement weight show a reduction in compressive strength by 12.62% and 3.89% respectively. On the other hand, both combination of admixtures can reach better performance on the final setting time which lead the slows the hydration process and provides adequate time to put concrete to the formwork. The results also show adequate correlations between compressive strength and the flexural strength. Furthermore, a prediction model is established the ratio of both value (𝑓𝑓𝑡𝑡𝑡𝑡𝑡𝑡/𝑓𝑓𝑐𝑐 ' ) based on the regression analyses, while it decreases obviously with the increase of compressive strength. It can be clearly that the ratio is strongly affected by compressive strength.

Development of a sustainable high early strength concrete incorporated with pozzolans, calcium nitrate and triethanolamine: An experimental study

High early strength concrete is a high-performance concrete that achieves a compressive strength of at least 20 MPa in 24 h. High early strength concrete becomes sustainable when pozzolans are incorporated. The best way to achieve sustainable high early strength concrete is the addition of chemical accelerators and pozzolans to conventional concrete. In this study the combination of 1 % calcium nitrate and 0.05 % triethanolamine is used as chemical accelerators. Three different types of Sustainable high early strength concrete are prepared: Ordinary portland cement with accelerators, Portland slag cement with accelerators, and ordinary portland cement replaced by 15 % Metakaolin with accelerators. The mechanical properties are determined through compressive strength, split tensile strength, and flexural strength. Durability performance was evaluated using rapid chloride permeability, water permeability, sorptivity, ultrasonic pulse velocity, sulphate resistance, chloride resistance, and acid resistance from day one to 270 days. In addition, characterization and microstructure analysis were studied using Scanning Electron Microscopy, Energy-Dispersive X-ray spectroscopy, and X-ray diffraction under chemical curing conditions. The experimental outcomes revealed that ordinary portland cement concrete substituted with 15 % Metakaolin and accelerators achieve early strength and durability performance, compared to ordinary portland cement with accelerators and Portland Slag Cement with accelerators.