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"high-strength concrete"
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Compressive Fatigue Investigation on High-Strength and Ultra-High-Strength Concrete within the SPP 2020
The influence of the compressive strength of concrete on fatigue resistance has not been investigated thoroughly and contradictory results can be found in the literature. To date, the focus of concrete fatigue research has been on the determination of the numbers of cycles to failure. Concerning the fatigue behaviour of high-strength concrete (HPC) and, especially, ultra-high-strength concrete (UHPC), which is described by damage indicators such as strain and stiffness development, little knowledge is available, as well as with respect to the underlying damage mechanisms. This lack of knowledge has led to uncertainties concerning the treatment of high-strength and ultra-high-strength concretes in the fatigue design rules. This paper aims to decrease the lack of knowledge concerning the fatigue behaviour of concrete compositions characterised by a very high strength. Within the priority programme SPP 2020, one HPC and one UHPC subjected to monotonically increasing and cyclic loading were investigated comparatively in terms of their numbers of cycles to failure, as well as the damage indicators strain and stiffness. The results show that the UHPC reaches a higher stiffness and a higher ultimate strain and strength than the HPC. The fatigue investigations reveal that the UHPC can resist a higher number of cycles to failure than the HPC and the damage indicators show an improved fatigue behaviour of the UHPC compared to the HPC.
Journal Article
Early-Age Cracking Resistance of Reinforced High-Strength Concrete
High-strength concrete (HSC) with a low water-cement ratio (w/c) may experience large autogenous shrinkage (AS). When shrinkage of concrete is restrained by the subgrade, foundation, or other part of the structure, HSC is more prone to crack. However, studies devoted to the early-age cracking resistance of reinforced HSC under uniaxial restrained conditions and adiabatic conditions are still lacking. In the current research, the effect of reinforcement percentage and reinforcement configuration on the temperature history, shrinkage, stress, and creep behavior of reinforced HSC at early age was analyzed using the temperature-stress test machine. Test results showed that reinforcement could effectively restrain the development of concrete shrinkage and creep. The cracking resistance of HSC increased with increasing reinforcement percentage, evaluated by the integrated criterion. With the same reinforcement percentage, reinforced HSC with distributed reinforcement along with a proper thickness of concrete cover exhibited higher cracking resistance compared with that of central reinforcement. Keywords: cracking resistance; early age; high-strength concrete (HSC); reinforcement; temperature-stress test machine (TSTM).
Journal Article
Fire Performance of Heavyweight Self-Compacting Concrete and Heavyweight High Strength Concrete
In this study, the fresh and hardened state properties of heavyweight self-compacting concrete (HWSCC) and heavyweight high strength concrete (HWHSC) containing heavyweight magnetite aggregate with 50, 75, and 100% replacement ratio, and their performance at elevated temperatures were explored experimentally. For fresh-state properties, the flowability and passing ability of HWSCCs were assessed by using slump flow, T500 mm, and J-ring tests. Hardened-state properties including hardened density, compressive strength, and modulus of elasticity were evaluated after 28 days of mixing. High-temperature tests were also performed to study the mass loss, spalling of HWSCC and HWHSC, and residual mechanical properties at 100, 300, 600 and 900 °C with a heating rate of 5 °C/min. Ultimately, by using the experimental data, rational numerical models were established to predict the compressive strength and modulus of elasticity of HWSCC at elevated temperatures. The results of the flowability and passing ability revealed that the addition of magnetite aggregate would not deteriorate the workability of HWSCCs and they retained their self-compacting characteristics. Based on the hardened densities, only self-compacting concrete (SCC) with 100% magnetite content, and high strength concrete (HSC) with 75 and 100% magnetite aggregate can be considered as HWC. For both the compressive strength and elastic modulus, decreasing trends were observed by introducing magnetite aggregate to SCC and HSC at an ambient temperature. Mass loss and spalling evaluations showed severe crack propagation for SCC without magnetite aggregate while SCCs containing magnetite aggregate preserved up to 900 °C. Nevertheless, the mass loss of SCCs containing 75 and 100% magnetite content were higher than that of SCC without magnetite. Due to the pressure build-up, HSCs with and without magnetite showed explosive spalling at high temperatures. The residual mechanical properties analysis indicated that the highest retention of the compressive strength and modulus of elasticity after exposure to elevated temperatures belonged to HWSCC with 100% magnetite content.
Journal Article
Punching-Shear Behavior of Glass Fiber-Reinforced Polymer-Reinforced Concrete Edge Column-Slab Connections: Experimental and Analytical Investigations
This paper presents test results from an experimental program conducted to study the punching-shear response of reinforced concrete (RC) edge column-slab connections (ECS connections) reinforced with glass fiber-reinforced polymer bars (GFRP). Five full-scale ECS connections were tested under vertical shear force and unbalanced moment until failure. Four of the five connections were reinforced with GFRP bars as flexural reinforcement; one connection was reinforced with steel bars for comparison. All slabs measured 2500 x 1350 x 200 mm (98.4 x 53 x 7.9 in.) with a 300 mm (11.8 in.) square column stub protruding 700 mm above and below the slab surfaces. The test parameters were flexural-reinforcement type, concrete strength, and moment-to-shear force ratio (M/V). The test results revealed that all the connections failed by punching shear with no signs of concrete crushing. The high-strength concrete (HSC) directly enhanced the punching-shear capacity, load-deffection response, and initial stiffiness of the connections. These connections also evidenced fewer and narrower cracks compared to their counterparts cast with normal-strength concrete (NSC). Increasing the M/V produced significant shear stresses, thereby reducing the vertical load capacity by 31% and 30% for the NSC and HSC connections, respectively. A simple design approach to predicate the punching-shear capacity of FRP-RC ECS connections is proposed. The proposed approach yielded good, yet conservative, predictions with respect to the available test data. Keywords: edge column-slab (ECS) connections; fiber-reinforced polymer (FRP); high-strength concrete (HSC); moment-to-shear force ratio (M/V); punching shear; shear strength prediction; two-way slabs.
Journal Article
Influence of Treatment Methods of Recycled Concrete Aggregate on Behavior of High Strength Concrete
Worldwide the concrete industry has started embracing the utilization of recycled concrete aggregates (RCAs) resulting from demolition and construction waste as full or partial substituents in the production of high-strength concrete (HSC) due to their economic and environmental benefits. Several parameters were experimentally investigated in this study. The first parameter analyzed the effect of replacing varying percentages of coarse aggregate with recycled aggregate. The second parameter examined the influence of two aggregate sizes (10 and 20 mm). The third parameter was intended for investigating the influence of three different RCA treatment methods utilizing sodium silicate immersion, cement slurry, and the Los Angeles (LA) abrasion simulation. The test results generally indicated degradation in the engineering properties of concrete produced using untreated RCA compared to the control. The degree of reduction increased as the replacement percentage was increased regardless of the aggregate size. The reduction in compressive strength appeared to have a more pronounced effect in comparison to the splitting tensile strength. The use of treated RCA improved concrete slump by 15–35%. This also caused enhancement in the engineering properties, especially for the LA abrasion mechanical treatment, which was very promising for both aggregate sizes. In comparison with the untreated RCA, the relative enhancement in water absorption was up to 76%, whereas splitting tensile and compressive strengths increased by 3–50% and 5–60%, respectively.
Journal Article
Rational Use of High-Strength Concrete in Flat Slab-Column Connections under Seismic Loading
High-strength concrete (HSC) slab-column connections with relatively low concrete strengths compared to today's capabilities have been tested under seismic-type loading in the past. Herein, the hybrid use of HSC with compressive strength approximately 120 MPa and normal-strength concrete (NSC) is investigated through three reversed horizontal cyclic-loading tests with different geometries of the HSC region and a reference NSC specimen. The results show that HSC applied in the vicinity of the column can significantly enhance the seismic performance of slab-column connections. The best result in terms of drift capacity and economic use of HSC was achieved in the case of full-depth HSC extended from the column's face up to 2.5 times the effective depth. Drift ratios up to 3.0% were achieved. A comparison with previous tests showed that the hybrid use of HSC and NSC can achieve similar results to the provision of punching shear reinforcement. Keywords: cyclic loading; flat plate; flat slab; high-strength concrete; hybrid; punching; seismic loading; slab-column connection.
Journal Article
Seismic Behavior of High-Strength Concrete Circular Columns Reinforced with Glass Fiber-Reinforced Polymer Bars
The linear elastic behavior of fiber-reinforced polymer (FRP) reinforcement makes it controversial to implement in seismic-resistant reinforced concrete (RC) structures. More concerns could be raised when such reinforcement is associated with high-strength concrete (HSC). Columns in multi-story buildings or bridges are common examples of structural members constructed using HSC. To date, all available research data on glass FRP (GFRP)-RC columns have shown that they have a maximum limit of concrete compressive strength equal to approximately 55 MPa (8000 psi). The results of five full-scale column-footing specimens are presented to study the seismic response of GFRP-RC columns, highlighting the effect of concrete compressive strength alongside other factors such as spiral pitch and axial load. It is concluded that when properly confined, GFRP-reinforced HSC circular columns can exhibit a stable seismic response with sufficient deformability. Moreover, several confinement and performance indexes were adjusted and evaluated to introduce an informative relationship for the design of GFRP-RC columns. Keywords: axial load level; circular columns; confinement index; glass fiber-reinforced polymer (GFRP); high-strength concrete (HSC); performance index; seismic loading; spiral pitch.
Journal Article
Vapor Pressure Modeling of High-Strength Concrete at High Temperatures
High-strength concrete (HSC) is susceptible to spalling at high temperatures. One reason for this is that vapor pressure builds up in concrete and plays a key role in spalling under certain conditions. However, vapor pressure modeling is still insufficient so far. Steam tables, which bear the actual states of water steam, have never been applied in vapor pressure modeling. In this paper, a meso-scale vapor pressure modeling approach using steam tables is presented. The effects of the thermal decomposition of the cement paste matrix and the vapor phase transfer driven by the gradient of vapor pressure are considered. By applying the theory of poromechanics, the Biot modulus is deduced and the mechanical effect of vapor pressure is modeled. Finally, the distribution and mechanical effect of vapor pressure in a 100 mm (3.94 in.) HSC cube specimen exposed to fre are modeled, and the applicability and effectiveness of the model are presented. Keywords: high-strength concrete; high temperature; modeling; spalling; vapor pressure.
Journal Article
Experimental Investigation of the Structural Behavior of Hybrid Fiber‐Reinforced High‐Strength Concrete Columns Under Eccentric Axial Loading
Numerous recent investigations have concentrated on improving the structural efficiency and reliability of concrete structural elements. This experimental study investigates the structural behavior of reinforced high‐strength concrete (HSC) columns incorporating hybrid steel‐polypropylene (PP) fibers under eccentric axial loading. Thirteen column specimens were tested to evaluate the effects of longitudinal and transverse reinforcement ratios, slenderness ratio, fiber type, and load eccentricity. The applied eccentricities corresponded to eccentricity‐to‐thickness (e/t) ratios of 0, 0.16, 0.34, 0.5, and ∞. Parameters such as vertical and lateral deformations, ultimate load capacities, failure modes, and ductility were measured and analyzed. Experimental results indicate that the hybrid fiber system enhanced both load capacity and deformation capacity compared to single‐fiber systems. Steel fibers (SF) contributed more significantly to the load‐bearing capacity, whereas PP fibers had a limited structural effect, primarily enhancing crack resistance and post‐peak ductility. Moreover, columns with hybrid fibers exhibited higher load capacity than those with only polypropylene fibers by up to 13.65%, while SF provided the primary contribution to load resistance. Increasing the longitudinal reinforcement ratio enhanced load capacity by up to 47%, whereas increasing the slenderness ratio reduced it by up to 26.9%. Increasing load eccentricity had the most pronounced effect, reducing axial capacity by up to ~83%. A load–moment (P–M) interaction diagram was developed based on the experimental results and showed reasonable agreement with code‐based predictions.
Journal Article