Conventional High Performance Concrete Research Articles

A comprehensive investigation on the impacts of steel slag aggregate on characteristics of high-performance concrete incorporating industrial by-products

Steel slag (SS), an industrial by-product of the steel industry, has the potential to serve as a natural aggregate alternative in concrete production to not only mitigate the exploitation of natural resources but also minimize the environmental impact of its treatment and disposal. This study was designed to investigate comprehensively the impacts of using SS as a full replacement for coarse aggregate and of using fly ash (FA) and ground granulated blast-furnace slag (GGBFS) as partial replacements for Portland cement on the engineering properties (i.e., workability, fresh unit weight, porosity, compressive and flexural strengths, ultrasonic pulse velocity, and drying shrinkage), durability (i.e., water absorption, surface electrical resistivity, and rapid chloride ion penetration), and microstructure (i.e., scanning electron microscopy observation) of high-performance concrete (HPC). A comparative analysis of the economic and environmental benefits of SS concrete versus natural aggregate concrete was also performed. The test results revealed that SS, FA, and GGBFS all impacted the properties of HPC significantly. The HPC mixtures in which natural aggregate had been completely replaced with SS exhibited about 20.4–21.3% higher unit weight than the natural aggregate concrete. The HPC samples with added FA and GGBFS exhibited enhanced performance in terms of mechanical strength, durability, and microstructure. Moreover, total material cost, global warming potential (GWP), and ozone depletion potential (ODP) were all found to be significantly lower in the HPC samples produced using SS and either GGBFS or a combination of FA and GGBFS. As a result, after 210 days of normal curing, the 100% SS concrete containing 15% FA and 35% GGBFS as a Portland cement substitution (S100F15G35 specimen) exhibited compressive and flexural strength values of 110.3 and 11.1 MPa, which were approximately 9.0% higher than the corresponding values of the reference concrete. Also, the S100F15G35 specimen registered the respective ultrasonic pulse velocity, surface electrical resistivity, and rapid chloride ion penetration values of 5328 m/s, 113.3 kΩ.cm, and 203 Coulombs, indicating high-quality and durable concrete. Moreover, incorporating 15% FA and 35% GGBFS in SS concrete resulted in a reduction of 15.7% drying shrinkage and 24.4% total material cost, especially reduced environmental impacts with a significant reduction in GWP and ODP by 43.5% and 29.2%, respectively. These findings further demonstrate the potential of using SS in combination with FA and GGBFS to create high-quality HPC that is both more economical and significantly more sustainable than conventional HPC.

Shear-bond behavior of nanocellulose-modified SHCC composite slabs: Translating material-level capacity into improved structural performance

Owing to their exceptional tensile properties, strain-hardening cementitious composites (SHCC) are indispensable for building and maintaining sustainable and resilient civil infrastructure. As such, to propel the structural implementation of SHCC, it is critical that their intriguing tensile characteristics be effectively translated into improved structural performance. Herein, we capitalize on the intrinsic pseudo-ductility of a novel SHCC—incorporating nanocellulose fibers and post-consumption glass powder (hereafter referred to as “nSHCC-GP”)—to mitigate shear-bond failure caused by the relative slip between steel and concrete in composite deck slabs. Twelve full-scale composite deck slabs, six with conventional high-performance concrete (HPC) incorporating steel mesh and six steel-mesh-free nSHCC-GP slabs, were subjected to monotonic bending. With the concrete for both slab sets designed for similar compressive strengths, the influence of concrete type (HPC or nSHCC-GP), decking profile (trapezoidal or reentrant), and shear span (520–770 mm) on the flexural capacity and shear-bond resistance was examined. The use of nSHCC-GP as a concrete topping improved the flexural capacity of composite slabs by >50 % and the shear-bond resistance by up to 40 %. Thus, the strain-hardening characteristics of nSHCC-GP were effectively translated into the structural scale, providing steel-mesh-free, high-performance composite deck slabs.

Prestressing low clinker structural concrete elements by ultra-high modulus carbon fibre reinforced polymer tendons

The combination of low clinker high-performance concrete (LCHPC) and ultra-high modulus (UHM) carbon fibre reinforced polymer (CFRP) tendons was recently proposed for prestressed structural elements. The 70% reduction in cement content resulting in limited creep and shrinkage of the LCHPC in comparison to a conventional high-performance concrete (HPC) and the very high UHM-CFRP tendon stiffness (> 509 GPa) were expected to impact the mechanical behaviour of such structures. This study focuses on the behaviour of 3 m-long beam specimens during prestressing, concrete hardening and in 4 point-bending experiments. Fibre optic sensors were implemented inside the CFRP tendons to measure strain during those stages and a digital image correlation system was employed to monitor the 4-point-bending tests. After 28 days, the LCHPC recipe, despite a 70% cement reduction and much smaller environmental footprint, did not show measurable differences in the prestress loss behaviour in comparison to a conventional HPC. The UHM-CFRP prestressing tendons, because of their stiffness, showed both higher prestress losses of around 40% and on average a nearly doubled prestress transfer length. However, they increased the beam`s maximum load-bearing capacity by 21% and showed 47% less deflection at failure in comparison to beams prestressed with the standard modulus (UTS)-CFRP tendons.

Mechanical Properties of High-Performance Concrete with Guinea Corn Husk Ash as Additive

Consideration on High Performance Concrete (HPC) has risen drastically because of the requirement for application of concrete volume with high strengths for construction work. In this study, the mechanical properties of HPC with Guinea Corn Husk Ash (GCHA) as supplement of cement was investigated. The proportioning of Ordinary Portland Cement (OPC) with GCHA is from 0 - 20%. Design of the concrete mix was done to achieve a characteristic strength of 50 N/mm². The chemical composition of the GCHA was determined using X-ray Fluorescence (XRF) Slump and compacting factor of fresh HPC were determined. Concrete cubes (for compressive strength), beams (for flexural strength) and cylinder (for split tensile strength) samples were cast and cured in water for 7 - 56 days. Density, compressive, flexural, and split tensile strengths were determined on the hardened HPC and were further examined using SEM analysis. Compressive strength at 56 days showed that control and inclusion of 5% GCHA gave strength 56.85 N/mm2 and 57.76 N/mm2, respectively above the designed target strength of 56.56 N/mm2 while inclusion of 10% GCHA met characteristics strength of 50 N/mm2. However, 5% GCHA-concrete had the highest flexural and split tensile strengths at 56 days of curing. Integration of 10% GCHA as replacement of OPC would produce concrete of higher strengths compared to conventional HPC at longer curing age. Based on the SEM results, uniform distribution of filler was obtained at 10% GCHA inclusion. At higher percentage of GCHA, resulting composite presents multiple and distinct grains with possible weak interfaces.

Comparative performance of conventional OPC concrete and HPC designed by densified mixture design algorithm

This experimental study evaluated the performance of normal ordinary Portland cement (OPC) concrete and high-performance concrete (HPC) that were designed by the conventional method (ACI) and densified mixture design algorithm (DMDA) method, respectively. Engineering properties and durability performance of both the OPC and HPC samples were studied using the tests of workability, compressive strength, water absorption, ultrasonic pulse velocity, and electrical surface resistivity. Test results show that the HPC performed good fresh property and further showed better performance in terms of strength and durability as compared to the OPC.

Influence of fiber content and reinforcement ratio on the water permeability of reinforced concrete

In service, reinforced concrete structures undergo various stresses inducing cracks. These cracks provide a preferential path for water and aggressive agents penetration into concrete, which compromises the structural durability by accelerating concrete and steel reinforcement deterioration. In this context, durability of cracked concrete has become an important research topic and can be studied through the permeability of concrete. This research project focuses on the influence of the fiber content and steel reinforcement ratio on the water permeability of reinforced concrete. Water permeability tests were carried out simultaneously with a uniaxial tensile loading applied on reinforced concrete prisms made of high performance concrete (HPC), high performance fiber reinforced concrete (HPFRC) and ultra high performance fiber reinforced concrete (UHPFRC). In service conditions, permeability is reduced by 31, 92 and 99 % for fiber contents of 0.75 % (HPFRC), 1.5 % (HPFRC) and 2 % (UHPFRC) respectively compared with conventional HPC. The increase of steel reinforcement ratio from 1.23 to 2.47 % reduced the permeability by 70 % at service loading.

Shear behavior of reinforced HPC beams made of a low cement content without shear reinforcements

High-performance concrete (HPC) usually has higher paste and lower coarse aggregate volumes than normal concrete. The lower aggregate content of HPC can affect the shear capacity of concrete members due to the formation of smooth fractured surfaces and the subsequent development of weak interface shear transfer. Therefore, an experimental investigation was conducted to study the shear strength and cracking behavior of full-scale reinforced beams made with low-cement-content high-performance concrete (LcHPC) as well as conventional HPC. A total of fourteen flexural reinforced concrete (RC) beams without shear reinforcements were tested under a two-point load until shear failure occurred. The primary design variables included the cement content, the shear span to effective depth ratio (a/d), and the tensile steel ratio (w). The results indicate that LcHPC beams show comparable behaviors in crack and ultimate shear strength as compared with conventional HPC beams. Overall, the shear strength of LcHPC beams was found to be larger than that of corresponding HPC beams, particularly for an a/d value of 1.5. In addition, the crack and ultimate shear strength increased as a/d decreased or w increased for both LcHPC beams and HPC beams. This investigation established that LcHPC is recommendable for structural concrete applications.

Early age setting, shrinkage and tensile characteristics of ultra high performance fiber reinforced concrete

Recently, ultra high performance fiber reinforced concrete (UHPFRC) with compressive strength over 180MPa and tensile strength of 10MPa has been developed. Since UHPFRC not only has superior strength, ductility and durability but also reduces the self weight of structures by decreasing the cross sectional areas needed, as such the research for applying UHPFRC to structural members is being widely performed. However, UHPFRC shows different material behavior to normal concrete and conventional high performance concrete. For example, it displays high early age autogenous shrinkage as well as rapid surface drying and surface cracking because of its low water–binder ratio and addition of high fineness admixtures. In this study, therefore, to precisely evaluate the basic material properties of UHPFRC at an early age, penetration resistance, shrinkage, tensile and ultrasonic pulse velocity (UPV) tests were performed. Test results indicate that paraffin oil well prevents the rapid water evaporation on the surface when the penetration resistance test of UHPFRC mortar was performed. The restrained shrinkage stress starts to develop when penetration resistance was 1.5MPa. Thus, the time-zero of autogenous shrinkage measurements of UHPFRC was defined as when the penetration resistance becomes 1.5MPa, this is 0.6 and 2.1h before the initial and final sets, respectively. The tensile strength and elastic modulus were measured from near the initial set using tensile test apparatus and prediction models for tensile strength and elastic modulus of UHPFRC were proposed. Finally, the UPVs at the proposed time-zero, initial and final sets were defined and the very early age strength developments were also predicted using UPV.

초고성능 섬유보강 콘크리트(UHPFRC)의 재료 특성 및 예측모델: (I) 응결 및 수축 특성과 인장거동 평가

Recently, ultra high performance fiber reinforced concrete (UHPFRC) having over 180 MPa compressive strength and 10 MPa tensile strength has been developed in Korea. However, UHPFRC represents different material properties with normal concrete (NC) and conventional high performance concrete (HPC) such as a high early age autogenous shrinkage and a rapid dry on the surface, because it has a low water-binder ratio and high fineness admixtures without coarse aggregate. In this study, therefore, to propose suitable experimental methods and regulations, and to evaluate mechanical properties at a very early age for UHPFRC, setting, shrinkage and tensile tests were performed. From the setting test results, paraffin oil was an appropriate material to prevent drying effect on the surface, because if paraffin oil is applied on the surface, it can efficiently prevent the drying effect and does not disturb or catalyze the hydration of cement. From the ring-test results, it was defined that the shrinkage stress is generated at the time when the graph tendency of temperature and strain of inner steel ring is changed. By comparing with setting test result, the shrinkage stress was firstly occurred as the penetration resistance of 1.5 MPa was obtained, and it was about 0.6 and 2.1 hour faster than those of initial and final sets. So, the starting time of autogenous shrinkage measurement (time-zero) of UHPFRC was determined when the penetration resistance of 1.5 MPa was obtained. Finally, the tensile strength and elastic modulus of UHPFRC were measured from near initial setting time by using a very early age tensile test apparatus, and the prediction models for tensile strength and elastic modulus were proposed.

Innovative design approach of precast–prestressed girder bridges using ultra high performance concrete

The construction of new bridges and the maintenance and renewal of aging highway bridge network using ultra high performance concrete can lead to the construction of long life bridges that will require minimum maintenance resulting in low life cycle costs. Ultra high performance concrete (UHPC) is a newly developed concrete material that provides very high strength and very low permeability to aggressive agents such as chlorides from de-icing salts or seawater. Ultra high performance concrete could enable major improvements over conventional high performance concrete (HPC) bridges in terms of structural efficiency, durability, and cost-effectiveness over the long term. A simplified design approach of concrete slab on UHPC girders bridge using the Canadian Highway Bridge Design code and the current recommendations for UHPC design is proposed. An illustrative example demonstrates that the use of UHPC in precast–prestressed concrete girders yields a more efficient design of the superstructure where considerable reduction in the number of girders and girder size when compared to conventional HPC girders bridge with the same span length. Hence, UHPC results in a significant reduction in concrete volume and then weight of the superstructure, which in turn leads to significant reduction in the dead load on the substructure, especially for the case of aging bridges, thus improving their performance.

Benefits of internal curing on service life and life-cycle cost of high-performance concrete bridge decks – A case study

This paper investigates the impact of internal curing on the service life of high-performance concrete (HPC) bridge decks by using analytical models to predict the times to onset of corrosion, onset of corrosion-induced damage, and failure of decks. Three bridge deck design options were compared: (i) normal concrete deck; (ii) HPC deck with supplementary cementing materials (SCM); and (iii) HPC deck with SCM and internal curing. It was found that the use of internal curing can extend the service life of high-performance concrete bridge decks by more than 20 years, which is mainly due to a significant reduction in the rate of penetration of chlorides in concrete as a result of reduced early-age shrinkage cracking and reduced chloride diffusion. Compared to normal concrete, HPC with SCM and internal curing was predicted to add more than 40 years to the service life of bridge decks in severe environmental conditions. Life-cycle cost reductions of 40% and 63% were estimated when conventional HPC and internally-cured HPC were used in bridge decks instead of normal concrete, respectively, despite the fact that the in-place unit cost of internally-cured HPC can be 4% higher than that of conventionally-cured HPC, which in turn can be up to 33% higher than that of normal concrete. This is due to a longer service life and less frequent maintenance activities offered by low-permeability HPC bridge decks.

Ductal – A High-Performance Material for Resistance to Blasts and Impacts

Reactive Powder Concrete (RPC) is a cementitious material consisting of cement, sand, silica fume, silica flour, superplastiser, water and high strength steel fibres. The material, developed by Bouygues the parent company of VSL, is marketed under the brand name of Ductal®. Production in Australia commenced in early 2003. Ductal is almost self placing, has a compressive strength of 160–200 MPa and a flexural strength of 30–40 MPa. In structural applications, Ductal is generally used without any passive reinforcement. Very fine high strength steel fibres are able to withstand secondary tensile stresses. Prestressing counterbalances the main tensile stresses due to bending. The durability properties of Ductal and its resistance to aggressive agents are orders of magnitude better than conventional high performance concrete. A predicted design life in marine environments of several hundred years is achievable. The unique characteristics of Ductal, including exceptionally high energy absorption capacity and resistance to fragmentation, make it ideal for panels and components that need to perform under explosives, impact or shock loads. The flexural toughness is greater than 200 times that of conventional fibre reinforced concrete. In May 2004, the performance of seven Ductal panels was evaluated in two large explosive trials performed at Woomera (South Australia). The panels performed remarkably well, exhibiting high levels of ductility and no signs of fragmentation. In further tests, 100mm thick Ductal blast resistant panels have been shown to effectively resist impacts by blast produced fragments using fragment simulated projectile tests. These panels can also withstand impacts from the highest class of rifle projectiles in the Australian Standard AS 2343. In June 2005, the first Ductal protective panels manufactured to provide resistance to blast were supplied to the Australian Government and installed on an Australian Government building in a high risk international location.

Effect of fly ash and slag on the fracture characteristics of high performance concrete

The premature deterioration of concrete structures in aggressive environments has necessitated the development of high performance concrete (HPC). The major difference between conventional concrete and HPC is essentially the use of chemical and mineral admixtures. The improved pore structure of HPC achieved by the use of chemical and mineral admixtures causes densification of paste-aggregate transition zone, which in turn affects the fracture characteristics. Hence, studies were taken up to investigate the effect of fly ash and slag on the fracture characteristics of HPC. Beam specimens (geometrically similar and single size variable notch) with locally available fly ash (25%) and slag (50%) as cement replacement materials were prepared and tested in a servo-controlled Universal Testing Machine (UTM) under displacement control. From the value of the peak load for each beam, various fracture parameters were calculated. The results show that there is a reduction in the fracture energy due to addition of fly ash or slag, which can be attributed to the presence of unhydrated particles of size larger than that of normal flaws in concrete. Also due to densification, the post peak behaviour is steeper for the fly ash or slag based HPC mixes. The results of the investigation are presented in this paper.