Concrete Mixtures Research Articles

Evaluating the fire resistance potential of functionally graded ultra-high performance concrete

Relevant standards stipulating the concrete surface temperature less than 380 °C and the defects of UHPC prone to fire spalling both limit the direct application of UHPC in specific tunnel fire prevention occasions. In view of this, a two-layered functionally graded ultra-high performance concrete (FGUHPC) was proposed in this paper, where lightweight aggregate concrete (LWAC) serves as the fire-resistant layer and UHPC functions as the structural load-bearing layer. The results showed that LWAC can control its backfire surface temperature to meet the standard requirements under a thickness of 40 mm, and the residual mechanical properties of UHPC before 400 °C were comparable to those at ambient temperature. The straight shear test was adopted to evaluate the FGUHPC interfacial bond strength. The results showed that the interfacial strength of FGUHPC reaches 3.05 MPa at ambient temperature, which is close to or even slightly higher than that of homogenous LWAC. When FGUHPC was treated at 1200 °C for 2h, FGUHPC can still maintains its integrity with its interfacial strength 120.0 % higher than that of LWAC. Compared to the homogenous UHPC member, FGUHPC composed of 40 mm LWAC and 120 mm UHPC effectively avoided explosive spalling, and maintained the interface temperature at around 200 °C. After static loading failure of the post-fire FGUHPC member, the two layers of concrete still remained bonded without delamination, and the loss in load-bearing capacity was less than 20 %. Finally, the design method of FGUHPC members under elevated temperature was discussed.

Удосконалення методу визначення коефіцієнта ущільнення асфальтобетонної суміші

Problem Statement. During sample preparation for reforming, there is a separation of cut mineral materials, which can affect the composition of the asphalt concrete mixture and lead to significant differences compared to the actual composition. The analysis of foreign sources revealed that the compaction coefficient is determined by the ratio of the average density of cores to the average density of samples made from the mixture used for constructing the road layer. A historical review of regulatory documents shows that the domestic method for determining the compaction coefficient has been in use for over 40 years. Additionally, a literature review found that this issue has not been adequately addressed. Thus, there is a need to study the effect of cut mineral material separation on the properties of reformed samples and the value of the compaction coefficient. Objective. To improve the method for determining the compaction coefficient of asphalt concrete mixture.

Performance Assessment of a Novel Green Concrete Using Coffee Grounds Biochar Waste

An actual scientific problem in current concrete science is poor knowledge of the problem of modifying concrete with plant waste. At the same time, plant waste benefits from other types of waste because it is a recycled raw material. A promising technological approach to modifying concrete with plant waste is the introduction of components based on the processing of coffee production waste into concrete. This study aims to investigate the use of biochar additives from spent coffee grounds (biochar spent coffee grounds—BSCG) in the technology of cement composites and to identify rational formulations. A biochar-modifying additive was produced from waste coffee grounds by heat treatment of these wastes and additional mechanical grinding after pyrolysis. The phase composition of the manufactured BSCG additive was determined, which is characterized by the presence of phases such as quartz, cristobalite, and amorphous carbon. The results showed that the use of BSCG increases the water demand for cement pastes and reduces the cone slump of concrete mixtures. Rational dosages of BSCG have been determined to improve the properties of cement pastes and concrete. As a result of the tests, it was determined that the ideal situation is for the BSCG ratio to be at a maximum of 8% in the concrete and not to exceed this rate. For cement pastes, the most effective BSCG content was 3% for concrete (3%–4%). The compressive and flexural strengths of the cement pastes were 6.06% and 6.32%, respectively. Concrete’s compressive strength increased by 5.85%, and water absorption decreased by 6.58%. The obtained results prove the feasibility of using BSCG in cement composite technology to reduce cement consumption and solve the environmental problem of recycling plant waste.

Lifecycle Assessment Analysis of Recycled Concrete Aggregate Incorporating Fly Ash and Hemp

The critical roles of recycling are increasing depending on depleted natural resources and its devastating consequences. Concrete has been one of the most used building materials for many years to response the basic need of human beings for shelter. The studies on the recycling of concrete are crucial to minimize negative effects of both the high amount of energy consumed during the production phase and the limited recycling opportunities after destruction. Considering the amount of construction and demolition waste (CDW) after the February 6, 2023 earthquakes in Türkiye, it is clear that recycling concrete (RC) may make a positive contribution to environmental sustainability and natural resources usage. In addition, as a result of the ongoing urban transformation projects throughout Türkiye, especially in Istanbul, there is a need to recycle CDW, the majority of which consists of concrete. This paper examines the equivalent CO2 emissions of recycled concrete aggregate (RCA) incorporation of various proportion fly ash and hemp based on previous studies by applying the Excel-based GreenConcrete LCA software developed at the University of California Berkeley Campus (UC Berkeley). As a result of the investigations, it is seen that the use of RCA, which is generated in large quantities both as a result of earthquakes and urban transformation projects, reflects positively on the environmental impacts in the LCA analysis. In addition, the use of concrete mixtures that contribute to the recycling of wastes such as fly ash and hemp used as admixtures contributes to reducing the environmental damage of these wastes and improving the concrete content.

Дослідження кольматувальної добавки та преспективи її застосування в дорожніх цементобетонах

ntroduction. Cement concrete, like most other porous materials, easily absorbs and retains moisture. Moisture can be absorbed by the reinforced concrete foundation if there are defects in the external waterproofing layer, leading to the development of mold, mildew, efflorescence, reinforcement corrosion, and damage to the finishing materials in the basement. The greatest danger is that frozen water expands and, through its pressure, destroys the structure from within. Waterproofing additives in cement concrete are used to improve the strength, corrosion resistance, impermeability, and frost resistance of concrete. Problem Statement. Ensuring the reliability of road pavement in the post-war period. Objective. To investigate the feasibility of using a waterproofing additive in a cement concrete mix using the example of the colmatant additive Penetron Admix.

Performance evaluation of high-performance concrete mixes incorporating recycled steel scale waste as fine aggregates

In this study, steel-scale waste (SSW), a byproduct generated during the manufacturing of steel, was investigated as a potential alternative to natural fine aggregates (sand) for preparing high-performance concrete (HPC). Three grades of sand and SSW with different particle sizes were mixed in varying combinations. Three different compaction techniques (loose, tamped, vibration) were employed. The optimum packing density for both SSW and natural aggregates was achieved using the vibration compaction method. Since the combination of 50 % sand and 50 % SSW exhibited the best packing density for both materials, this bi-grade aggregate mixture was selected for the mix preparation. The mechanical tests (compressive strength, flexural strength) and durability assessment (bulk water sorptivity, rate of water absorption, chloride ion penetration) were performed to achieve the desired objectives. The specimens were exposed to two different curing regimes i.e., normal curing and heat curing at elevated temperature. A significant increase in compressive and flexural strength was observed with the increased content of SSW. A compressive strength as high as 140 MPa was obtained for the HPC mix containing SSW aggregates and steel fibers. The replacement ratio of SSW was optimized to achieve better strength and durability. Experimental results showed that heat curing was more effective than conventional curing methods in improving the performance of the concrete.

Compressive stress-strain response of freshly compressed rubberized concrete: An experimental and theoretical study

Although using crumb tire rubber concrete (CTRC) in constructing structural elements is accompanied by various environmental and economic advantages, it always comes with challenges due to a significant loss in some mechanical properties of this concrete type. To tackle this challenge, a novel technique of compressing fresh concrete was used, and its impacts on improving the mechanical features of CTRC were investigated. For this purpose, concrete specimens containing crumb tire rubber (CTR), as the fine aggregate substitute, were constructed considering the variables of the water-to-cement ratio (w/c), volume percentage of CTR, and the fresh concrete pressure level as a fraction of steel tube (mold) yielding stress. After the application of a specified short-term pressure to the fresh mix inside the steel molds and the time required for the concrete setting, the steel tubes were removed after curing, and the concrete core alone was exposed to an axial compressive load. According to the test results, the mechanical properties, weight loss resulting from compressing the fresh concrete, energy absorption, failure pattern, the concrete microstructure, water absorption, and porosity were evaluated. By applying an initial axial pressure of 25–80 MPa on the mixes containing 0 %, 15 %, and 30 % CTR replacing the fine aggregate, the compressive strength, the ultimate strain, the toughness, and the initial modulus of elasticity experienced 100–140 % increase, 130–420 % increase, 120–1140 % increase, and 66–70 % decrease, respectively, compared with the uncompressed specimen. Finally, a regression analysis was employed to propose prediction models for the compressive capacity, modulus of elasticity, peak strain, ultimate strain, and relative toughness of freshly compressed concrete containing CTR particles; these models show proper agreement with the experimental results.

Flexural cracking behavior of steel-NC-UHPC composite beam under negative bending moment

Steel-concrete structures are widely applied in bridge engineering due to their superior mechanical performance and cost-effectiveness. However, normal concrete (NC) decks often suffer cracking problems, adversely affecting their serviceability. Ultra-high performance concrete (UHPC) can be used to partially replace the top of NC decks to enhance their post-cracking behavior because UHPC shows high tensile strength, strain-hardening characteristics in tension, and strong bond strength with NC. To this end, this paper focused on the flexural behavior of steel-NC-UHPC composite beams regarding their failure mode, stiffness, strain development, cracking behavior, crack width, etc. Test results indicated that the test specimens mainly exhibited two types of failure modes: shear failure of the NC layer and local buckling of the compressive flange at the steel girder, which were mainly determined by the reinforcement ratio. Flexural stiffness was controlled by the steel girder, and the reinforcement ratio had a notable effect on the reinforcement strain and crack propagation. Additionally, cracks can be categorized into three types: through cracks, connecting cracks, and separate cracks. These cracks in the UHPC layer and NC layer would affect each other, especially those near the roughening interface. The sectional nonlinear analysis was employed to calculate the strain of reinforcement and the steel girder accurately. Finally, the prediction methods of crack width for the NC layer and UHPC layer were discussed. Formulas in NF P18–710 were verified to be feasible for the prediction of UHPC crack width. The UHPC influence factor was introduced to modify the calculation results of the NC crack width by the Chinese NC code.

The potential of solid waste as a viable replacement for quartz sand in the ultra-high performance concrete: a comprehensive review

ABSTRACT Ultra-high performance concrete (UHPC) is renowned for its dense structure and exceptional mechanical properties, including durability. However, its widespread adoption is hindered by the high costs of essential fine aggregates like quartz sand and the associated environmental impact. Additionally, using industrial solid waste raises pollution concerns, contradicting global sustainability goals. Numerous studies have shown that it is feasible to produce eco-friendly UHPC with excellent performance by solid waste. This comprehensive review thoroughly investigates the workability, mechanical properties (including compressive strength, flexural strength and tensile strength), microstructure (encompassing pore structure and interfacial transition zone) and durability of UHPC incorporating solid waste in its production. The paper emphasizes the critical influence of factors, such as the solid waste substitution rate and the physical and chemical properties of solid waste. The paper also outlines the current application of UHPC with solid waste in pavement engineering and highlights the urgent need to address challenges such as high production costs, the lack of design standards and construction technique deficiencies, thereby emphasising the urgency surrounding the design and advancement of solid waste-incorporated UHPC in pavement engineering as it can reduce the environmental impact of traditional UHPC and improve the efficient use of solid waste.

Exploring Current Techniques for Improving the Properties of New Concrete

In modern construction, the properties of new concrete are crucial for building quality and structural performance. Recent technological advancements have led to significant progress in enhancing the properties of new concrete. This study employs theoretical and experimental methods to explore the connection among shear stress and shear strain rate under vibration, the impact of aggregate substitution on concrete performance, and the rheological properties of moist shotcrete. The findings suggest that adjusting mix proportions and using additives can significantly improve concrete's strength, durability, and workability. This research provides engineers with a theoretical foundation for optimizing concrete mixtures and construction techniques, thereby improving overall building quality and construction efficiency. The findings suggest that sustainable materials can be used without compromising structural integrity, making the construction process more environmentally friendly while maintaining high performance standards. Furthermore, this study highlights the importance of understanding concrete behavior under various conditions to develop more resilient and long-lasting structures.

Investigation of Performance Specifications for Marshall Mixes Using Performance-Based Mix Design Methodology

This paper presents a comprehensive study for developing the performance specifications for the Marshall mixes using the performance-based mix design (PMD) methodology. The specification describes the desired levels of fundamental engineering properties for predicting performance during mix design or quality assurance checks at the time of construction. In this study, the bituminous concrete mixture was designed through complementing volumetric criteria with performance tests such as dynamic creep and the indirect tensile asphalt cracking test for evaluating resistance against rutting and fatigue cracking, respectively. This study considers different factors such as five different types of design aggregate gradations (mid-gradation, fine-coarse gradation, coarse gradation, coarse-fine gradation, and fine gradation), three binder types (VG-30, VG-40, and PMB-40), and five levels of compactive efforts (35, 50, 75, 90, and 110 blows on each face). The study finds the effect of design aggregate gradation, binder type, and compactive effort on the rutting and cracking resistance of bituminous mixes. The research study also comprehends the influence of volumetric properties on the performance parameters. Further, it establishes the initial performance criteria for rutting and cracking for Marshall mixes. The performance space diagram (PSD) has also been plotted, portraying the overall performance (acceptable, desirable, or unsatisfactory performance regions) of bituminous mixtures based on rutting resistance and cracking resistance. This paper highlights and advocates the integration of these performance-based specifications into the Marshall mix design specifications for improving pavement characteristics and extending overall service life.

Performance of concrete beams strengthened with FRP rods: A review

Ductility is a critical property in structural engineering, ensuring that beams can undergo significant deformation before failure, thereby giving plenty of notice before disastrous collapse. This study investigates the ductility properties of constructions that have been reinforced using FRP rods, which are increasingly popular due to their corrosion resistance, superior strength with low mass, and durability. Traditional steel reinforcement has well-documented ductility properties, but FRP bars, due to their brittle nature, pose challenges in achieving the desired ductility levels in structural applications. This research evaluates various factors influencing FRP-reinforced beams' ductility, including the type of FRP material, the hybridization of FRP with other reinforcing materials, and the effect of utilizing fibres in the mixtures to enhance the mechanical characterstics of concrete. Studies have indicated that the ductility of beams can be enhanced using hybrid rebar systems, which integrate steel and fibre reinforced polymer. However, complex and expensive production methods limit their practical application. Using steel bars with FRP bars can significantly incresese seriviceability requiremts such as crack width and deflection, but they also lower corrosion resistance, especially in aggressive environments. The beams' overall ductile behavior is primarily determined by the concrete's characteristics. Fibres greatly increase the mechanical characteristics, toughness, and ductility of the concrete mix, strengthening the bond between bars and the concrete and improving the overall performance of the beam.

Out-of-plane performance of BFRP reinforced UHPC thin panel: experiment and numerical analysis

In this study, the out-of-plane performance of ultra-high performance concrete (UHPC) thin panels reinforced with basalt fiber reinforced polymer (BFRP) bars was investigated. Eight panels were tested under four-point load, with the investigating parameters including panel thickness, reinforcement ratio, and the presence of steel fibers. The failure mode, crack pattern, load vs. mid-span displacement, and reinforcement strain relationships were studied. Test results revealed that panels with a higher thickness (70 mm) exhibited 178.6% higher initial stiffness, 34.5% higher cracking loads, and 88.7% higher peak loads compared to those with a lower thickness (50 mm). The effects of a larger reinforcement ratio and the presence of steel fibers became more pronounced after concrete cracking, leading to 21.2% and 22.1% higher post-cracking stiffness, respectively. Adding steel fibers helped control the development of diagonal cracks and shifted the panel failure mode from shear to flexural failure. Based on the comparison of test results with design codes, the expressions in CAN/CSA-S806-12 were recommended for predicting the load-carrying capacity of the specimens. Furthermore, a two-dimensional finite element (FE) model was developed to reproduce the test results, which validates the adopted CDP model for UHPC and the bond-slip behaviors between UHPC and BFRP bars.

Carbonation and chloride penetration performance of self-compacting concrete with masonry and concrete wastes

In this research, masonry and concrete construction and demolition wastes (CDWs) were used as supplementary cementitious material (25% vol. residue of masonry, RM) and recycled coarse aggregate (RCA) in increasing levels (0%, 50% and 100% vol. residue of concrete), respectively, in the development of self-compacting concrete (SCC). The performance of SCC mixtures was evaluated in terms of fresh properties, compressive strength, resistance to both accelerated (1% CO2, 65% R.H. and 23 °C temperature) and natural carbonation as well as chloride penetration. Experimental results showed a monotonic workability reduction associated to the incorporation of increasing levels of RCA. In compressive strength, the SCC with RCA showed the greatest increase in this mechanical property after 28 days of accelerated exposure in the carbonation chamber, when compared to its water-cured counterpart. Yet, at 360 days of accelerated carbonation exposure, all SCCs showed compressive strength reductions compared to their water-cured counterparts. On the other hand, the chloride permeability resistance of the SCCs was low and very low at the ages evaluated. Thus, the findings of this study indicate that the use of CDW can generate SCCs with adequate fresh properties, compressive strength and carbonation and chloride penetration performance, which offers benefits for the environment.

A novel approach to assess internal pore structure and quantify tortuosity of clogged pervious concrete through image analysis techniques

ABSTRACT The major objective of this research was to develop an innovative approach to characterise the pore structure of pervious concrete (PC) mixtures and quantify tortuosity in pre- and post-clogged conditions through 2D and 3D image analysis. Four different types of PC mixtures were prepared and subjected to computed tomography (CT) scanning to retrieve morphological information covering over 1900 images, followed by tortuosity quantification of each of 200 interconnected pore paths using vascular modelling toolkit (VMTK). The porosity of PC obtained from laboratory-based tests was 10–25% lower than image analyses. Further, along the depth of PC, a significant decrease in the number of pores in the top 60–80 mm was observed due to clogging, which revealed that maintenance be adopted only in the top 80 mm. Control and clogged PC with smaller sized aggregates and lower w/c ratio were more tortuous compared to higher w/c ratio while opposite for larger sized aggregates, ascribed to the occurrence of shorter interconnected pore paths comprising larger pore diameter, remarking that permeability will depend on both tortuosity and path diameter. CT scanning was used in predicting tortuosity and pore interconnectivity of PC through VMTK approach extensively used in medical science and seldom used in engineering.

Elastic Modulus Prediction of Ultra-High-Performance Concrete with Different Machine Learning Models

Elastic modulus, crucial for assessing material stiffness and structural deformation, has recently gained popularity in predictions using data-driven methods. However, research systematically comparing different machine learning models under the same conditions, especially for ultra-high-performance concrete (UHPC), remains limited. In this study, 10 different machine learning models were evaluated for their capacity to predict the elastic modulus of UHPC. The results showed that XGBoost demonstrated the highest accuracy in predictions with large training datasets, followed by KNNs. For smaller training datasets, Decision Tree exhibited the greatest accuracy, while XGBoost was the second-best performing model. Linear regression displayed the lowest accuracy. XGBoost demonstrated the most potential for accurately predicting the elastic modulus of UHPC, particularly when a comprehensive dataset is available for model training. The optimized XGBoost exhibited better predictive performance than fitting equations for different UHPC formulations. The findings of this study provide valuable insights for researchers and engineers working on the data-driven design and characterization of UHPC.

Assessing the Impact of Recycled Concrete Aggregates on the Fresh and Hardened Properties of Self-Consolidating Concrete for Structural Precast Applications

This study explores the influence of different concentrations of recycled concrete aggregate (RCA) on the fresh and hardened properties of self-consolidating concrete (SCC) in order to assess the structural suitability of the use of RCA in a precast concrete plant. The study particularly emphasizes the early strength of the produced concrete. The RCA was sourced from crushed concrete used in roadway applications and was sieved to replicate the characteristics of natural aggregate. Five different SCC mixes were produced, with RCA substituting 0%, 10%, 30%, 50%, and 70% of the natural coarse aggregate (NCA) by weight. For each different mix design, the hardened properties tested were the compressive strength and tensile strength. The fresh properties investigated were the passing and filling ability. Additionally, aggregate properties including grain size distribution and absorption of coarse aggregate were studied. The selected mix design follows a typical well-graded self-consolidating concrete mix with 28-day strength of 8000 psi (55.16 MPa). It was found that replacing up to 50% of the NCA with RCA improves the early strength of concrete without a significant impact on the fresh and hardened concrete properties.

The interplay among particle packing, binder, and strength: amelioration of ultra-high performance concrete with nanomaterials, a hope or hype?

A Middling quality of concrete exacerbates deterioration that tarnishes structural integrity and leads to dilapidated infrastructures. The significant intent of this work is to develop sustainable Ultra-High-Performance Concrete (UHPC) using nanosilica and nano clay. The factors, such as particle size, shape, and particle packing effect plays a key role in development of eco-friendly UHPC. Elkem Materials Mixture Analyser (EMMA), based on Modified Andreasen and Andersen particle packing theory is employed for mix optimization to attain dense packing with low binder content. UHPC is amalgamated with cement, silica fume, nanosilica, and nano clay in various combinations. The mix combination includes control mix (A0), B1–B3 that holds 1–3% nano silica, and C1–C3 yields 1–3% nano clay. It is inferred, B3 (3% nanosilica) exhibits the highest compressive strength of 118 MPa due to its size, quasi spherical shape, and homogenous dispersion. Consequently, C2 (2% nanoclay) manifest 18 and 33% enhancement in splitting tensile and modulus of rupture due to due to layered shape of nano clay that acts as reinforcement, inhibits cracks, and improves strength Microstructural analysis confirms the formation of additional hydration products with less voids. Thus, synergy of particle size, shape, and packing effect results in sustainable UHPC.

Radiation shielding properties of sustainable concrete with novel plastering techniques

In concrete applications. Major/critical applications of such concrete are radiation-shielding facilities. Both steel slag and silica fume are examples of common by-product materials that can be used as a replacer of aggregates and cement. Thus, in this research work, steel slag was utilized as heavy aggregate in concrete production besides silica fume to present sustainable concrete mixtures probably with better radiation-shielding properties. Different cementitious plasters were applied on the conducted sustainable concrete mixture using different powdery materials; hematite, magnetite, barite, bentonite, and steel slag powders in addition to nano-titanium dioxide as full replacers for sand. The proposed plasters were presented to determine the optimum plaster technique in terms of static performance and attenuation capability against gamma and neutron radiations. The results exhibited that utilizing steel slag and silica fume in concrete mixtures enhanced compressive strength by up to 9.09 % compared to conventional concrete, while the addition of nano-titanium to conventional plaster led to superior enhancement in the compressive strength by up to 38.65 % relative to traditional plaster. Conversely, fully replacing conventional silica sand with the abovementioned powdery materials generally reduced the compressive strength of cementitious plasters by up to 30.83 %. However, the radiation shielding properties against Cs-137, and Co-60 energies have been enhanced by up to 20 % and 26 %, respectively.

A Mesoscale Comparative Analysis of the Elastic Modulus in Rock-Filled Concrete for Structural Applications

Rock-filled concrete (RFC) is an advanced construction material that integrates high-performance self-compacting concrete (HSCC) with large rocks exceeding 300 mm, providing advantages such as reduced hydration heat and increased construction processes. The elastic modulus of RFC is a critical parameter that directly influences its structural performance, making it vital for modern construction applications that require strength and stiffness. However, there is a scientific gap in understanding the effects of rock size, shape, arrangement, and volumetric ratio on this parameter. This study investigates these factors using mesoscale finite element models (FEMs) with spherical and polyhedral rocks. The results reveal that polyhedral rocks increase the elastic modulus compared to spherical rocks, enhancing RFC’s load-bearing capacity. Additionally, a 5% increase in the elastic modulus was observed when the rockfill ratio was increased from 50% to 60%, demonstrating a direct correlation between rock volume and mechanical performance. Furthermore, the elastic modulus rises significantly in the early stages of placement, followed by a gradual increase over time. Optimal rock sizes and a balanced mix of rock shapes allow for improved concrete flow and mechanical properties, making RFC a highly efficient material for construction. These findings offer valuable insights for designers and engineers looking to optimize RFC for structural applications.