Concrete Strength Calculation Model Based on the Neutralization Depth Stratification of Concrete

Bond durability and degradation mechanism of GFRP bars in seawater sea-sand concrete under the coupling effect of seawater immersion and sustained load

The conventional design method of concrete mix ratio relies on a large number of tests for trial mixing and optimization, and the workload is massive. It is challenging to cope with today's diverse raw materials and the concrete's specific performance to fit modern concrete development. To innovate the design method of concrete mix ratio and effectively use the various complex novel raw materials, the traditional mix ratio test method can be replaced with the intelligent optimization algorithm, and the concrete performance prediction can be realized rapidly and accurately. The mixed ratio of the rubber fiber concrete was designed with its 28-day strength test. Then the range and variance analysis of the orthogonal test results were carried out to determine the optimal mix ratio and its influencing factors. A data set containing 114 sets of valid test data was collected by combining the rubber concrete mix test data published in recent years. Based on this data set, there are six influencing factors; rubber content, rubber particle size, and polypropylene fiber content are considered as the input variables, and the 28-day concrete compression, splitting tensile, and flexural strength are considered as the output variables. A strength prediction model of rubber fiber concrete is established based on the extreme learning machine (ELM). For verifying the ELM prediction model's performance, this article has conducted a comparison experiment between this model and other intelligent algorithm models. The results show that the model has the advantages of high accuracy and high generalization ability compared with other algorithm models such as conventional neural networks. It can be used as an effective method for predicting concrete performance. The method allows for the innovation and development of concrete mixing technology.

In this work, the durability of the E-glass/epoxy was investigated in terms of degradation in tensile properties and microstructure. Specimens were conditioned in seawater under sustained load and without load at 23 °C, 45 °C and 65 °C for the period of 15 months. The tensile strength of the E-glass/epoxy reduced gradually with immersion time. It reduced by 11% from 811 MPa to 721 MPa and by 18.2% from 811 MPa to 663 MPa for samples immersed without load and with 15% sustained load respectively. The respective reduction for 23°C and 45°C was 1.1% and 5.5% for samples without load and 6.2% and 11.3% for samples immersion under 15% sustained load after 15 months of exposure. The failure strain of E-glass/epoxy composite was slightly affected for the samples immersed without load during the period of 15 months but it was more noticeable under 15% sustained load at 65°C when the tensile strain reduced to 1.65% after 15 months of immersion. Furthermore, Scanning Electron Microscopy (SEM) analysis was conducted to evaluate the degradation of fiber matrix interface. Results revealed that moisture, temperature and sustained load have a deteriorative impact on the performance of the composite.

Effect of silica fume inclusion on the strength, shrinkage and durability characteristics of natural pozzolan-based cement concrete

Alkali-activated cements prepared from aluminosilicate powders, such as blast furnace slag and fly ash, are rapidly attracting attention as alternatives to cement because they can significantly reduce CO2 emissions compared to conventional cement concrete. In this study, we investigated the relationship between the physical and chemical changes by accelerated carbonation conditions of alkali-activated cements. Alkali-activated cements were prepared from binders composed of blast furnace slag and fly ash as well as alkali activators sodium silicate and sodium hydroxide. Physical changes were analyzed from compressive strength, pH, and neutralization depth, and chemical changes were analyzed from XRD, TG-DTG, and 29Si MAS NMR. The C–(N)–A–S–H structure is noted to change via carbonation, and the compressive strength is observed to decrease. However, in the case of Na-rich specimens, the compressive strength does not decrease by accelerated carbonation. This work is expected to contribute to the field of alkali-activated cements in the future.

Investigation of long-term tension stiffening mechanism for ultra-high-performance fiber reinforced concrete (UHPFRC)

Biogenic sulfur attack in a reinforced concrete sewage treatment plant. Re-visited mechanism and rehabilitation proposal

Effect of sustained service loads on the self-healing and corrosion of bacterial concretes

Objective: The objective is to determine the effect of treated RCA on the mechanical strength of hardened concrete, and determine the influence of treated RCA on water transport within the matrix of hardened concrete. Aim: The study aims to use pozzolanic concentration of cement and RHA slurry to pretreat coarse RCA for full replacement of NCA for sustainable concrete production. Background: One of the common modes of disposal of construction waste is strained landfills. This study proposes a constructive way of recovering the coarse aggregates of recycled aggregates from laboratory concrete waste taken through a focused treatment process with pozzolan. The study aims to replace the proportions of the cement slurry to treat and replace with rice husk ash (RHA) for the modification of recycled concrete aggregate (RCA) and replace fully natural coarse aggregate (NCA) for sustainable concrete production. One of the main challenges of recycled concrete aggregate (RCA) is the fractured surface, which often results in reduced strength and loss of concrete durability. The strength of concrete with RCA is principally influenced by the fractured hardened paste attached to the surface, predominantly characterized by voids and gaps resulting from its production using a mechanical method. High water penetration within and around the aggregate matrix due to the presence of micro- and macro-cracks results in strength and durability deterioration of concrete. Methods: This study addresses these problems by specifying aggregate treatment with a pozzolanic slurry of cement and RHA. This was conducted in two (2) phases; first, to determine the optimum proportion of cement slurry concentration (0, 20, 40, 60, 80, and 100%), and second, to increase the silicate formation in cement slurry by substituting the proportions of cement with RHA (0, 5, 10, and 15%). The performance of concrete was evaluated by mechanical strength (compressive and split tensile strength) at 7, 28, and 56 days and water transport within the concrete (surface suction and submergence) at 28 and 56 days of curing age. Results: The use of cement slurry treatment at various concentrations generally increased compressive strength at 28 days compared to untreated RCA. The findings show that at a 20% concentration of cement slurry, the increase in compressive strength is 38.4%. Upon replacement of cement in treatment slurry of RCA with 5% RHA, the increase in compressive strength was 61%, while the split tensile strength increased by 10.2%. The amount of water absorbed was observed after 30 minutes of full submergence in water, indicating that samples with 20% cement concentration at 28 days resulted in the lowest water absorption of 2.01%. However, with the replacement of 5% RHA, the water absorption slightly increased to 2.3%, but still less than the requirement of 3.5%. The corresponding test results for water suction by capillarity, initial and secondary sorptivity coefficients (Si and Ss) were found to be 0.0330mm/√sec. (1.98mm/√hr.) and 7.95×10−4mm/√sec. (0.04mm/√hr.) respectively, all less than 6mm/√hr requirement. This improved performance was attributed to the increased strength and structure of the interfacial transition zone (ITZ) around the RCA. Conclusion: Based on the results of mechanical strength and water transport, characteristics of the new concrete were improved when coarse RCAs were pretreated with 20% pozzolanic concentration containing cement and RHA. The use of a pozzolanic treatment slurry containing 15% cement and 5% RHA to treat coarse RCA can produce concrete with characteristics similar to those of natural concrete aggregates. This study presents a methodological utilization and improvement of RCA wastes for field application.

This study investigates the post-thermal mechanical performance of concrete incorporating clamshell powder (CSP) as a partial cement replacement at 0%, 4%, 6%, and 8% by weight. Grade M20 concrete specimens were tested for workability, rebound hardness, compressive strength, and splitting tensile strength at ambient temperature and after exposure to elevated temperatures of 150 °C, 300 °C, and 400 °C. Results showed that workability decreased progressively with higher CSP content due to increased water absorption and coarser particle texture. At ambient conditions, the highest compressive strength (40.35 MPa) was recorded for 8% CSP, an 51.63% improvement over the control mix. Thermal exposure up to 300 °C enhanced compressive strength by approximately 12.2%, attributed to matrix densification and improved bonding, while exposure to 400 °C caused a slight reduction (3.93%) due to microcracking and C–S–H decomposition. Splitting tensile strength peaked at 6% CSP and 300 °C (2.86 MPa), 75.5% higher than the control specimen CS0 (1.63MPa) at the same temperature. A strong positive correlation (R² = 0.72) was observed between compressive and tensile strengths. The findings demonstrate that optimal CSP incorporation (6–8%) can improve both compressive and tensile performance after moderate heat exposure, offering a sustainable and thermally resilient alternative to conventional cement in structural applications.

The influence of mineral admixtures on the short and long-term performance of concrete

Climate changes have been an issue to consider in the last few years. In this research, the performance of self-compacting concrete in simulated hot weather conditions is investigated. Test parameters included the ambient temperature, induced materials temperature, and the use of a retarder. The rheological properties, early shrinkage, and compressive strength were determined for different test parameters. The performance enhancement due to cooling the concrete materials and the use of a retarder was assessed and quantified. The results showed that the use of a retarder had an adverse effect on the compressive strength between 7 and 90 days in simulated hot weather conditions. The J-ring outputs were the most improved due to cooling SCC materials. On the other hand, V-funnel time T5 and the 28-day compressive and tensile strength were the least improved. The use of a retarder further reduced the compressive and tensile strength improvement percentage and increased the percentage enhancement of V-funnel T5 time.

High temperatures can induce a range of physical and chemical alterations in radiation-protective concrete, potentially compromising its strength and significantly diminishing its radiation shielding capabilities. Therefore, it is very important to study the high temperature performance of radiation-proof concrete to ensure its safety and stability in extreme environment. In this study, the magnetite-serpentine radiation-proof concrete is designed with magnetite as coarse aggregate, serpentine as fine aggregate, and Portland cement and granulated blast furnace slag as mixture. The apparent characteristics, mass loss, ultrasonic pulse velocity, mechanical properties, shielding performance, and correlation of this concrete were analyzed through experiments. The results show that the damage degree and relative wave velocity have a good correlation in evaluating the relative mass loss, linear attenuation coefficient, compressive strength, and tensile strength after high temperatures. The compressive strength at 800 °C is 12.2 MPa and the splitting tensile strength is 0.48 MPa; the linear attenuation coefficient of specimen at 800 °C is reduced to 80.9% of that at normal temperature. Meanwhile, penetrating cracks appeared at 600 °C and spalling phenomenon appeared at 800 °C, and better thermal stability and favorable mechanical properties and shielding performance also occurred; thus, suitable radioactive and high temperature environment was determined. The results could provide scientific guidance for nondestructive testing and performance evaluation of shielding structure materials.

The deterioration of concrete structures is mainly due to the combined action of the environment and external load. In this study, 32 reinforced concrete columns were prepared to evaluate the coupling actions on the properties of reinforced concrete structures. The durability, bearing capacity, and failure mode of reinforced concrete columns were investigated under the combined action of freeze-thaw (F-T) cycles, sustained load, and salt corrosion (water or composite salt solution). Results show that the mass fluctuation of reinforced concrete columns under a sustained load was more obvious during F-T cycles. During the early F-T cycles, the sustained load was beneficial to the F-T resistance of the reinforced concrete columns. With the increase in F-T cycles, the damage to the columns with a sustained load gradually aggravated. In the composite salt solution, the damage to the reinforced concrete columns was postponed, and its durability showed a two-stage evolution. After 100 F-T cycles, the mass loss and relative dynamic modulus of elasticity (RDME) deterioration of the columns with a sustained load sped up significantly. The combined action of salt corrosion, load, and F-T cycles has the most significant influence on the bearing capacity, stiffness deterioration, and crack development of reinforced concrete columns.

The objective of this experimental study is to explore the impact of utilizing two kinds of lightweight aggregates ،as partial substitutions for natural coarse aggregate ،on the porous concrete mechanical performance. The study focuses on splitting tensile, compressive and flexural strength tests of such type of concrete incorporated pumice and LECA at a replacement volumetric ratio of 10%. The effect of internal curing provided by the lightweight aggregates on compressive strength was also examined. To enhance the mechanical performance styrene butadiene rubber (SBR) was added to selected mixes. The results obtained showed that replacing natural coarse aggregate with LECA significantly increased compressive strength while pumice led to a reduction. The inclusion of SBR further improved compressive strength particularly in the LECA mix under dry curing conditions where a maximum strength of 15.4 MPa was recorded. Although the incorporation of both lightweight aggregates initially led to a decline in tensile and flexural strengths, the addition of SBR effectively minimized these losses resulting in significant improvements especially in mixes containing pumice. Furthermore, the LECA mix under dry curing achieved a compressive strength of 10.7 MPa relative to 8.8 MPa for the reference mix which highlights the benefits of internal curing via pre-wetted lightweight aggregates. Overall, the findings obtained suggest that the combination of LECA and SBR delivers superior mechanical performance making it a promising solution for parking lots, pavers, and light traffic roads.