Resistance Of High Strength Concrete Research Articles

The Resistance of High Strength Concrete with Diatomaceous Earth As Cement Replacement to Nacl Attack

High strength concrete (HSC) requires high amount of cement in order to make it more dense and compact. Using diatomaceous earth (DE) is an alternative to reduce the cement content in HSC. In this study the DE was used as cement replacement at the 0%, 5%, 10% and 15% replacement levels. The water to binder ratio was 0.3. The type F superplasticizer at 1.5% of cement weight was added. The DE was first ground, sieved with sieve #200 and calcined at 600°C for 5 hours before it used as cementitious material. The 50 mm cube specimens were prepared, cured in the water for 28 days, and then immersed in 10% NaCl solusion. After 1 and 2 months of immersion period, the surface visual appearance, mass and compressive strength of the specimens were examined and compared with the unimmersed specimens. The surface visual appearance shows that the HSC with 15% has smallest damaged as well as smallest degradation of compressive strength. However, the smallest mass loss was obtained at the HSC with 5% DE content.

Effect of nanomaterials additives on performance of concrete resistance against magnesium sulfate and acids

Abstract This paper is dedicated to study the effect of nanomaterials, represented by Nano-SiO2 (NS) and Nano-Metakaolin (NMK), on the absorption, total porosity, magnesium sulfate resistance and acid resistance of High Strength Concrete (HSC) and High-Performance Concrete (HPC). An experimental study was carried out on three grades of concrete (55 MPa, 80 MPa and 90 MPa) with cement content of 350, 450 and 600 kg/m3 and water/binder ratio of 0.45, 0.29 and 0.24 respectively. The considered dosages of NS is 0.5%, 1%, 1.5% and 2% by weight of cement as an addition, whereas these dosages were 1%, 3%, 6% and 9% in case of NMK. Some of concrete specimens were immersed in 10% magnesium sulfate solution and the other specimens were immersed in nitric acid and sulfuric acid after 7 days of water curing, where the pH value for each used acid was 1.0. The magnesium sulfate and acids resistance were evaluated in terms of compressive strength loss, expansion strain, weight loss, and Ultrasonic Pulse Velocity (UPV) loss. The relation between compressive strength loss and each of expansion strain, weight loss and UPV loss were also studied. In addition, to judge the cost effectiveness of concrete with and without NS subjected to magnesium sulfate attack, the cost of compressive strength for each one MPa was determined for different concrete grade levels. The tests results have shown a pronounced increase in compressive strength as a result of using nanomaterials at different ages. Moreover, adding NS and NMK has revealed a remarkable reduction in water absorption and porosity of HSC and HPC. Furthermore, the use of NS and NMK enhances the magnesium sulfate resistance and both nitric and sulfuric acid resistance (1.0 pH value) with different concrete grade levels.

Improving resistance of high strength concrete (HSC) bridge beams to frost and defrosting salt attack by application of hydrophobic agent

HSC (High Strength Concrete) is increasingly used for bearing bridge structures nowadays. Bridge structures in the Czech Republic are exposed to severe conditions in winter time and durability of the concrete is therefore a crucial requirement. The high strength and low water absorption of HSC suggests that the material will have high durability. However, the situation may not be so straightforward. We carried out a study of the very poor durability of HSC concrete C70/85 used to produce prestresed beams 37.1 m in length to build a 6-span highway bridge. After the beams were cast, a production control test indicated some problems with the durability of the concrete. There was a danger that 42 of the beams would not be suitable for use. All participants in the bridge project finally decided, after extensive discussions, to attempt to improve the durability of the concrete by applying a hydrophobic agent. Paper will present the results of comparative tests of four hydrophobic agents in order to choose one for real application and describes this application on construction site.

Mechanical behavior and chloride penetration of high strength concrete under freeze-thaw attack

This paper proposes an experimental study to investigate the freeze-thaw (FT) effects on mechanical behavior and chloride diffusion in high strength concrete. Sets of high strength concrete cubes are cyclically frozen in range from +18°C to −20°C. The mechanical property and the chloride penetration tests are performed on the specimens after 0, 5, 10…95, and 100 FT cycles. FT effects on surface scaling damage, compressive strength, elastic modulus, stress-strain relationship and chloride resistance of high strength concrete are clarified. Also, a simple model is discussed and verified to predict the chloride concentration of high strength concrete attacked by FT cycles. Results show that the behavior of high strength concrete depends on the number of FT cycles. Visible damages appear in concrete after about 40 FT cycles. Before 25–60 FT cycles, no significant difference exists in FT-caused weight loss between normal strength concrete and high strength concrete. Beyond this, the FT-caused weight loss in normal strength concrete becomes faster than that in high strength concrete. FT damage decreases the compressive strength, the elastic modulus and the chloride resistance of concrete, but increases its ductility. In the present test, the compressive strength and elastic modulus decrease about 32% and 24% after 100 FT cycles, respectively. The surface chloride concentration and chloride diffusion coefficient increase to about twice of the control values.

Freeze–thaw durability of high strength concrete under deicer salt exposure

Freeze–thaw resistance of high strength concrete (HSC) and normal strength concrete (NSC) mixes with varying air contents was investigated by moisture uptake, mass loss and internal damage measurements. Sufficiently air-entrained HSC mixes demonstrate significant improvement in salt frost scaling resistance and the characteristics of air-void system is not a major factor. This can be attributed to the reduced capillary porosity and connectivity which curtails ice-growth promoted by capillary suction of surface liquid under freezing. A clear bi-linear pattern is found for the mass loss and moisture uptake curves of HSC mixes, the transition point of which coincides with each other. This demonstrates the importance of initial moisture condition in concrete prior to F–T test. Increased imperviousness of HSC to moisture ingress renders it more prone to long-term frost damage intrinsically, which is evidenced by much higher initial freezing strain in HSC from the length-change measurement on thin specimens at various degrees of saturation levels.

The detection of high-strength concrete exposed to high temperatures using infrared thermal imaging technique

Based on the detection principle regarding physical and chemical changes of the internal structure of concrete at elevated temperatures, and with the application of infrared thermal imaging technique, laboratory investigations related to infrared thermal image inspection and compressive strength test on C80 high-strength concrete (with or without polypropylene fibres) were carried out under thoroughly heated conditions. With the application of SEM and XRD analysis, the microstructure and organisational structure of the concrete could be seen. Also, data analysis could help identify their relationship in cases with polypropylene fibres added or not. The results showed that the elevated temperature through infrared images generally exhibits an upward trend with increasing temperature. Only slight damages were detected below 400°C, whereas more and more severe deterioration events were expected when the temperature was over 500°C. Meanwhile, the compressive strength kept decreasing as the temperature increased. Additionally, the addition of polypropylene fibres with appropriate length, diameter and quantity contributed to the improvement of high-temperature resistance of high-strength concrete.

Corrosion Resistance of High Strength Concrete Containing Palm Oil Fuel Ash as Partial Cement Replacement

This experimental work investigates the influence of POFA as partial cement replacement towards corrosion resistance of high strength concrete. Plain high strength concrete (P0) with 100% ordinary Portland cement (control specimen) and POFA high strength concrete containing POFA as partial cement replacement material were used. At the first stage, mix with 20% POFA (P20) has been identified as the best performing mix after cubes (150×150×150 mm) containing various content of POFA as partial cement replacement were prepared, continuously water cured and subjected to compressive strength test at 28 days. At the second stage of study, control specimen (P0) and high strength concrete mix containing 20% POFA (P20) were prepared in form of cylinders with reinforcement bar buried in the middle for corrosion resistance test. Specimens were subjected to half cell potential technique following the procedures outlined in ASTM C876 (1994). Incorporation of POFA as partial cement replacement has contributed to densification of microstructure making the concrete denser thus exhibit higher resistance towards corrosion as compared to plain concrete.

Experimental Study on Impermeability and Frost Resistance of High Strength Concrete Used in Shaft of Coal Mine

This paper presents results of impermeability and frost resistance tests of a series of high strength concrete which will be used in Yuncheng coal mine shaft lining. And the shaft is one of the most difficult to construct using freezing method because of the extreme thick overburden soil. The results show the impermeability and frost resistance of the selected concrete mix proportion options can meet the special requirements of the shaft construction. It’s due to the low water-cement ratio, admixture and water-reducing agent decreases void caused by excess water. And the composite mineral admixture forms bubbles to cut off the tiny water permeable channels in cement stone. Also the filling effect and pozzolanic effect caused by fly ash contribute a lot. The research on high strength concrete used in shaft of coal mine with thick overburden soil is still rare worldwide.

Construction application of Fibre/Mesh method for protecting concrete columns in fire

In this paper, a construction application of a technique to improve the fire resistance of high strength concrete is presented. Before the construction application, fire tests of three hours duration were carried out in accordance with ISO-834. Three types of mitigating methods, namely, a specimen with no protection (control), with fireproof panel protection and with the combination of polypropylene fibre reinforcement and metal mesh confinement (Fibre/Mesh), were applied to full sized columns for comparison purposes. The fire resistance performance of all columns was tested under loads. After the fire tests, the severity of spalling of specimens was assessed, and the best performing technique, Fibre/Mesh, for spalling protection was selected for an application in practice. The process of the construction application is described in detail, including pumping, pouring and compacting of the concrete. The concrete quality was examined and the behaviour of the concrete was observed. Consequently, it was verified that this new spalling resistance technique is feasible in practice.

Degradation of permeability resistance of high strength concrete after combustion

To evaluate the remaining durability of concrete materials after combustion, the permeability of high strength concrete (HSC) after combustion was studied. The transport behavior of chloride ion, water and air in concrete after combustion and the effect of temperature, strength grade, and aggregation on the permeability of HSC after combustion are investigated by chloride ion permeability coefficient (Dc), water permeability coefficient (Dw) and air permeability coefficient (Da). The experiment results show that all three permeability coefficients commendably reflect changes of permeability. The permeability coefficient increases with the evaluation temperature. After the same temperature, the permeability coefficient of HSC is lower than that of normal strength concrete (NSC). However, the degree of degradation of permeability coefficient of HSC is greater than that of NSC. The permeability resistance of HSC containing limestone is better than that of HSC containing basalt. Combining changes of compressive strength and permeability, the remaining durability of concrete materials after combustion is appropriately evaluated.

Fibrous Reinforcing System to Increase the Shear Resistance of High Strength Concrete

The available research has evidenced that discrete steel fibers can increase significantly the shear resistance of High Strength Concrete (HSC) structural elements when High Strength Fiber Reinforced Concrete (HSFRC) is designed in such way that fiber reinforcing mechanisms are optimized. In general, the increase of the concrete compressive strength is associated to an increase of its compactness, resulting benefits in terms of durability, but a strong concern emerges related to the integrity of this material, since it fails in a too brittle mode when submitted to high temperatures. To contribute for the knowledge about the benefits provided by discrete steel fibers when added to HSC applied to laminar structures, an experimental program composed of slab strips submitted to shear loading configuration was carried out. Uniaxial compression tests with cylinders of 150 mm diameter and 300 mm height, and bending tests with 600×150×150 mm3 beams were executed to assess the compression and bending behavior of the developed HSFRC. To evaluate the influence of the percentage of fibers in the shear resistance of laminar structures, three point loading tests with slab strips of 800×170×150 mm3 dimensions were performed. Taking the obtained experimental results, the applicability of the formulation proposed by RILEM TC 162-TDF was evaluated. Test results showed that, even with relative low dosages of steel fibers, the increment in shear resistance was significantly increased. The main obtained results in the research program are presented and discussed in this paper.

The influence of aggregate type on the strength and abrasion resistance of high strength concrete

Abstract This paper examines the influence of aggregate type on the strength characteristics and abrasion resistance of high strength silica fume concrete. Five different aggregate types (gabbro, basalt, quartsite, limestone and sandstone) were used to produce high strength concrete containing silica fume. Silica fume replacement ratio with cement was 15% on a mass basis. Water-binder ratio was 0.35. The amount of hyperplasticizer was 4% of the binder content by mass. Gabbro concrete showed the highest compressive and flexural tensile strength and abrasion resistance, while sandstone showed the lowest compressive and flexural tensile strength and abrasion resistance. High abrasion resistant aggregate produced a concrete with high abrasion resistance. Three-month compressive strengths of concretes made with basalt, limestone and sandstone were found to be equivalent to the uniaxial compressive strengths of their aggregate rocks. However, the concretes made with quartsite and gabbro aggregate showed lower compressive strength than the uniaxial compressive strength of their aggregate rocks.

Influence of Mineral Admixtures on Crack Resistance of High Strength Concrete

As high strength concrete (HSC) is widely used in construction, more and more attention has been paid to crack resistance of it. In order to improve crack resistance of HSC, we study the influence of mineral admixtures (ground slag, silica fume and fly ash) on brittleness and characteristic length as crack resistance’ indexes. Testing researches shows, without admixture, crack resistance of HSC is the lowest; when one of the three mineral admixtures added, crack resistance increases dramatically; when two of the three mineral admixtures are added in the concrete, crack resistance increases a little more and it does not change very much no matter which two are mixed; crack resistance comes out the highest when the three mineral admixtures are added in concrete. Mechanism analysis shows, Adding fine and high active ground slag, silica fume and fly ash into concrete can greatly improve microstructure of transition zone, decrease Ca(OH)2, ettringite and porosity in concrete, increase C-S-H gel and greatly reduce the original micro-cracks in the transition zone.

Mechanical properties and microstructure of high strength concrete containing polypropylene fibres exposed to temperatures up to 200 °C

High strength concrete has been used in situations where it may be exposed to elevated temperatures. Numerous authors have shown the significant contribution of polypropylene fibre to the spalling resistance of high strength concrete. This investigation develops some important data on the mechanical properties and microstructure of high strength concrete incorporating polypropylene fibre exposed to elevated temperature up to 200 °C. When polypropylene fibre high strength concrete is heated up to 170 °C, fibres readily melt and volatilise, creating additional porosity and small channels in the concrete. DSC and TG analysis showed the temperature ranges of the decomposition reactions in the high strength concrete. SEM analysis showed supplementary pores and small channels created in the concrete due to fibre melting. Mechanical tests showed small changes in compressive strength, modulus of elasticity and splitting tensile strength that could be due to polypropylene fibre melting.

Consideration of the Effect of Miscellaneous Factors on Frost Resistance of High Strength Concrete by Using the Factorial Design Method

Factorial design method is applied to investigate the effects of various factors simultaneously rather than to conduct a series of single-factor experiment. As the results, frost resistance of the concrete specimens, in both W/C ratio of 0.28 and 0.35, was highly affected by the type of coarse aggregate that is, andesite produced more durable concrete than the limestone. Durability factor of the specimens, with W/C ratio of 0.28, which were demolded after I day and transferred to the curing room was higher than those demolded after 2 days. This stated the efficiency of the high early curing in high strength concrete.

Reliability Bases for High-Strength Concrete Columns

High-strength concrete (HSC) has found its main application in the lower columns of high-rise buildings. Due to its large application, type of failure, and importance to structural integrity, the reliability assessment of HSC columns is an extremely important issue. On the other hand, this assessment is a very involved issue. First, a unique formulation of the failure criterion has not yet been established. Second, the moment magnification method, when applied to slender HSC columns, may produce conservative or unconservative estimates of the load effects depending on the load eccentricity. Third, information on the resistance variability of HSC columns is scarce. In this paper, the basic requirements for reliability analysis of HSC columns are presented. A failure criterion is sought, a procedure that does not resort to the moment magnification method is established for the computation of the load effects on slender columns, and probabilistic descriptors of load and resistance of HSC are investigated.

Creep, shrinkage, frost, and sulphate resistance of high strength concrete

A comprehensive study was undertaken to determine the shrinkage, creep, and durability of high strength concrete (50–70 MPa) containing silica fume and lignite fly ash. The concrete mixtures contained normal CSA type 10 (ASTM type 1) portland cement, 10% condensed silica fume, and different amounts of fly ash that varied between 0 and 80% of the weight of binder in the mixture. The aggregates-to-binder ratio by weight was maintained at 5 and the weight of the superplasticizer was varied between 1.5% and 2.2% of the binder while the water-to-binder ratio was maintained at 0.27. The test program consisted of compressive strength tests at various ages on concrete cylinders; drying shrinkage tests at room temperature; creep tests of sealed and unsealed concrete at room temperature (21 °C (70°F)) and at high temperatures (up to 232 °C (450°F)) under three different stress regimes; frost resistance tests on concrete prisms up to 300 freezing and thawing cycles; and sulphate resistance tests on concrete prisms immersed in 5% Na2SO4 solution for up to 10 months. The results indicated that up to 60% fly ash replacement with 10% silica fume showed either superior or similar 28- and 56-day compressive strengths when compared with the 100% cement control mixture. Fly ash + silica fume concrete indicated lower shrinkage and long-term creep. Creep increased with increase in temperature due to physico-chemical processes, which were confirmed by microstructure analysis using the scanning electron microscope. The creep and shrinkage data of high fly ash + silica fume concrete fitted well to the current ACI creep and shrinkage model. Replacement of cement by up to 35% fly ash and 10% silica fume indicated enhanced frost resistance, without any air-entrainment. The addition of 8% air-entrainment to the 20% fly ash + 10% silica fume mixture increased the durability factor by about 10%. For the 50% fly ash + 10% silica fume mixture, the frost durability factor was found comparable to that of the 100% cement control mixture, and air entrainment did not improve its value appreciably. Sulphate resistance of concrete made with 100% CSA type 10 cement was found satisfactory; however, with increasing fly ash contents (up to 50%), the expansion due to sulphate action was suppressed. A study of matrix morphology and microstructure bonding, using the scanning electron microscope, helped to explain the observed results in a comprehensive manner. Key words: creep, shrinkage, compressive strength, frost resistance, durability factor, sulphate resistance, fly ash, silica fume, high-strength concrete, SEM micrograph, matrix morphology.