Papers by Keyword: High Strength Concrete

Abstract: The paper presents the results of measurement of resistance of concrete with surface treatment against water with deicing chemicals. Surface treatment of the test specimens was performed by sandblasting using steel balls. The effect of sandblasting was measured on normal strength aerated concrete (NC) and high strength concrete (UUHPC). Aerated concrete gains its resistance to water with deicing chemicals mainly due to its pores structures, while UUHPC due to the low porosity and low water absorption of the cement matrix. The sandblasting of the specimens simulated the required surface finish or mechanical deterioration of the concrete.

Abstract: The Brazilian disc test with central notch is widely used to evaluate mixed mode I/II fracture resistance of brittle materials such as rocks and concrete. An analytical evaluation is used based on the maximum tangential stress (MTS) criterion and the generalised maximum tangential stress (GMTS) criterion. In this contribution two concrete types, a C 50/60 and a high strength concrete, were compared using the GMTS criterion. Also, the influence of critical distance r_C on the fracture resistance under the mixed mode I/II was studied.

Abstract: In an effort to reduce the amount of cement in the concrete industry and produce greener concrete, emphasis was put on using several industrial by-products such as silica fume, fly ash and slag as partial replacements for cement in concrete. Due to the enormous number of mega reinforced concrete projects constructed in the United Arab Emirates, it is considered to be one of the largest consumers of high strength concrete in the region. On the other hand, only limited research has been done on high strength concrete incorporating local materials in the UAE. The main objective of this research is to conduct an investigation on the performance of high strength concrete containing silica fume as partial replacement of ordinary Portland cement incorporating superplasticizers and local UAE materials by studying its mechanical properties and durability. The experimental program involved two groups: The first group had a water-to-binder material ratio (w/b) of 0.4, whereas, the second group had w/b = 0.3. For both groups the silica fume replacement percentages were 0 (control mix) 5, 7.5, 10, 12.5, and 15 percent. The mechanical properties were tested at 7, 28, and 91 days and the durability tests were performed at 28 days. The results were compared to the control mix and they showed that for all the curing ages studied the use of silica fume as partial replacement of OPC has favorable effect on the compressive strength values and the optimum replacement ratios of silica fume for the tested specimens are found to be at 12.5% and 10% replacement for the w/b ratios of 0.3 and 0.4, respectively. For all the four performed durability tests the replacement of the OPC with silica fume is found to have favorable results and the higher the silica fume percentage replacement of OPC the more favorable the results are. The detailed description of the used mixes and the main conclusions drawn from this research are presented in this paper

Abstract: Use of high strength concrete (HSC) becoming inevitable in case of modern structures, which require application of advanced materials. High strength of concrete can be reached by higher dose of cement or addition of various kinds of fibres as a dispersed reinforcement. In practice are most commonly used steel, glass and polypropylene fibres, but basalt fibres are still under investigation. Basalt is highly resistance to aggressive chemicals and stable in high temperatures in comparison to other materials used for dispersed reinforcement. This study focuses on use of chopped basalt fibres in purpose to enhance properties of harden concrete. Six mixes with various dose of cement and chopped basalt fibres were designed for evaluation of properties of fresh and hardened concrete. As it was expected, chopped basalt fibres have negative influence on workability of fresh concrete but in comparison to other types of fibres the decrease is not that dramatic. Test results indicate increase of compressive strength after 28 days and even higher gain of strength after 90 days in case of mixes with addition of chopped basalt fibres. Reduction of strength due to exposure to 400 and 800 °C is also evaluated and in case of 400 °C temperature exposure the results are very promising.

Abstract: This issue mainly studied the compressive strength and weight loss of high strength concrete in sulfuric and acetic acid attack. Different substitution amounts of silica fume and fly ash single single incorporated and co-incorporated in cement to form high strength concrete. Then weight losses, XRD and SEM were carried out to investigate compressive strength and acid resistance corrosion mechanism after leaching in 5% H₂SO₄ and 5% CH₃COOH solution for 28 days. The results show S10F12 improves the compressive strength by 29.6%, 40.5% and 28.4% in 7, 28 and 56 days curing respectively compared to OPC. The improvement of resistant to 5% H₂SO₄ and 5% CH₃COOH of S10F12 is 38.3% and 112.5% for 28 days immersion respectively, and S10f12 still has compressive strength of 58.8 MP and 45.9 MPa under 5% H₂SO₄ and 5% CH₃COOH attack while OPC only has 38.8MPa and 21.6 MPa after 28 days immersion.

Abstract: High strength concrete has become a design requirement in recent years due to increase in number of infrastructure projects. This paper presents the effect of incorporating Ultra Fine Slag (UFS) and steel fibre to obtain high strength concrete. To achieve target strength of about 80 MPa, it is proposed to the replacement of cement of 10%, 20% and 30% with UFS and incorporating 0.5% and 1.0% fibre in concrete. An experimental investigation is carried out to find the mechanical properties of the concrete. From the test results, it was observed that a compressive strength of 95 MPa was achieved at 30% replacement of cement with UFS and 1.0% fibre content. In addition, there was a significant improvement in split tensile strength and flexural strength of the concrete. This study demonstrates that a high strength concrete can be obtained from partial replacement of cement with UFS and addition of steel fibre.

Abstract: The use of high strength concrete (HSC) in multi-story buildings has become increasingly popular. Selection of HSC over normal strength concrete (NSC) allows for reducing the dimensions of the columns sections. However, this reduction has consequences on the structural performance in case of fire, as smaller cross sections lead to faster temperature increase in the section core. Besides, HSC experiences higher rates of strength loss with temperature and a higher susceptibility to spalling than NSC. The fire performance of a column can thus be affected by selecting HSC over NSC. This research performs a comparison of the fire performance of HSC and NSC columns, based on numerical simulations by finite element method. The thermal and structural analyses of the columns are conducted with the software SAFIR^®. The variation of concrete strength with temperature for the different concrete classes is adopted from Eurocode. Different configurations are compared, including columns with the same load bearing capacity and columns with the same cross section. The relative loss of load bearing capacity during the fire is found to be more pronounced for HSC columns than for NSC columns. The impact on fire resistance rating is discussed. These results suggest that consideration of fire loading limits the opportunities for use of HSC, especially when the objective is to reduce the dimensions of the columns sections.

Abstract: The idea of recycling concrete waste as coarse aggregates for new concrete construction is gaining importance on the international scale but the studies on durability performance of Recycled Aggregate Concrete (RAC) are limited. There is a little or no work carried out on high strength recycled aggregate concrete. This study was an attempt to investigate and compare the acid resistance of the RAC and Natural Aggregate Concrete (NAC) of grade M50. In the present experimental investigation, concrete specimens of 0% and 50% RAC were prepared, cured and immersed in H₂SO₄ solution at 3% concentration at 7 and 28 days respectively. The period of exposure was varied from 3 days to 56 days. The loss of weight, compressive and tensile strengths of the specimens were found to be higher when RAC is exposed to acidic environment compared to NAC.

Abstract: This paper presents a research to produce high strength concrete incorporated with fly ash as cement replacement up to 50% (high volume fly ash concrete) by using local material. The research is conducted by testing the strength development of high volume fly ash concrete at the age of 14 days, 28 days and 56 days. As a control mix, the compressive strength of Ordinary Portland Cement (OPC) concrete without fly ash is used. Both concrete mixtures use low w/c. consequently, they lead to the use of 1 % superplasticizer to reach sufficient workability in the process of casting. The specimens are concrete cubes with the dimension of 15 cm x15 cm x 15 cm. The totals of 24 cubes of HVFA concrete and OPC concrete are used as specimens of testing. The compressive strength design of concrete is 45 MPa and the slump design is ± 10 cm. The result shows that the compressive strengths of OPC concrete at the age of 14 days, 28 days, and 56 days are 38 MPa, 40 MPa, and 42 MPa. Whereas the compressive strength of HVFA concrete in the same age of immersing sequence are 29 MPa, 39 MPa, and 42 MPa. The result indicates that HVFA concrete can reach the similar compressive strength as that of normal concrete especially at the age of 56 days by deploying low water cement ratio.

Abstract: The dynamic mechanical properties (stress-strain diagram, ultimate stress, ultimate strain and strain rate) and of high strength concrete (HSC) with 5% and 10% silica fume (SF) addition at high strain rate of 10 s^-1 to 10² s^-1 (3.8 MPa, 4.1 MPa and 4.8 MPa) are determined using Split Hopkinson Pressure Bar equipment. The compressive strength of the HSC at design strength of 80 and 90 MPa is also determined. Results show that the compressive strength of the 5%SF and 10%SF HSC are 83 MPa and 92 MPa, respectively. The dynamic stress-strain diagrams show that the higher the pressure load, the higher the values of ultimate dynamic stress, σ_u and the ultimate strain rate, ἐ_u for both percentages of SF addition concrete. The ultimate dynamic stress, σ_u are between 200 – 250 Mpa and the ultimate strain rate, ἐ_u is in the range of 95 s^-1 and 160 s^-1. The ultimate dynamic strain, ε_u between 0.005-0.008 mm/mm. The dynamic increase factors (DIF) of the HSC are more than 2 compare to normal strength concrete.