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Effect of silica fume and steel fibers on some properties of high-strength concrete

Abstract The main disadvantage of high-strength concrete is its highly brittle behavior and this can beovercome by adding fibers to the concrete. This would also improve some other mechanical properties of high-strength concrete such as tensile strength and compressive strength. These properties are not very well established for high-strength steel-fiber reinforced concrete (HSFRC) yet. In this study the influence of silica fume on the properties of HSFRC were investigated by using silica fume of two different percentages and three different hooked-end fibers namely, 30/0.50, 60/0.80 and 50/0.60 length/diameter (mm/mm). Fibers were added to concrete in three different volume percentages of 0.5, 1.0 and 2.0 by volume of concrete. The results indicated that there is a linear function between splitting tensile strength (Fsplt) and volume percentage of fibers (Vf) [i.e. Fplt = A(Vf) + B, where A and B are correlation coefficients] as well as between splitting tensile strength (Fsplt) and compressive strength (Fc) of plain series A concrete [i.e. Fsplt = C (√Fc) + D, where C and D are correlation coefficients]. These relations can describe the development of splitting tensile strength of HSFRC containing no silica fume, 5% silica fume and 10% silica fume by weight of cement. On the other hand, although silica fume has an effect on compressive strength, volume percentage and aspect ratio of steel fibers has little effect.

Cement mixtures containing copper tailings as an additive: durability properties

The effects of copper tailings as an additive, on some durability properties of cement mixtures were investigated. In each mixture, copper tailings addition levels by mass were 0%, 5% and 10%. Compared to the control samples, copper tailings blended pastes showed superior performance against autoclave expansion while insignificant decreases in sulfate resistance of mortars were observed. Copper tailings increased the water absorption and total permeable voids of concretes slightly. However, the compressive and flexural strengths of blended concretes were higher than those of the control samples. Similarly, improved resistance to acid attack and chloride penetration as the copper tailings content of concretes increased were also observed. Results further showed that the ASTM C 1202 rapid chloride permeability test may not be a valid indicator of chloride migration in mixtures containing conductive copper tailings. These results suggest that copper tailings can potentially enhance the durability properties of cement based materials.

Effects of Silica Fume and Steel Fibers on Some Mechanical Properties of High-Strength Fiber-Reinforced Concrete

There are many test methods to measure the impact resistance of fiber-reinforced concrete that are complicated, time consuming, and expensive. A practical test method has been developed to measure the impact resistance of high-strength fiber-reinforced concrete (HSFRC). The equipment developed can also be used for testing aggregate impact values by simply changing the base plate of the machine. A machine was developed to measure the surface abrasion resistance of HSFRC. Testing fiber-reinforced concrete for surface abrasion resistance was found to be extremely difficult if realistic and practical results were desired. In this study the influence of silica fume on the properties of HSFRC was investigated by using silica fume at two different percentages and with three different hooked-end fibers, namely, 30/0.50, 60/0.80, and 50/0.60 length/diameter (mm/mm). Fibers were added to concrete in three different percentages of 0.5, 1.0, and 2.0% by volume of concrete. The results show that including fibers in high-strength concrete improves impact resistance, surface abrasion, and splitting tensile strength.

Rheology, strength and durability properties of mortars containing copper tailings as a cement replacement material

This paper investigates the suitability of copper tailings as a cement replacement material in mortars. The impact of copper tailings at 0%, 5%, 10% and 15% cement replacement level by mass on the rheology, mechanical and durability properties of mortars was evaluated. Results revealed higher yield stress and flow loss in mixtures incorporating copper tailings. High mortar compressive strength, flexural strength and abrasion resistance were determined at 5% cement replacement level. Furthermore, despite increased rate of water absorption, higher resistance to acid attack and chloride penetrations were also observed in samples containing copper tailings. These improved properties were more pronounced in samples containing pre-wetted tailings at 5% cement substitution level. The use of copper tailings in mortars could bring about significant environmental conservation and sustainability gains.

Seismic Performance Assessment of a Corroded 50-Year-Old Reinforced Concrete Building

AbstractDeterioration due to corrosion becomes a more serious problem when future earthquakes with unpredicted intensity and time are considered. Therefore, the prediction of performance levels of corroded reinforced concrete structures is important to prevent serious premature damage. In this study, a corroded, 50-year-old high school building was analyzed by considering corrosion effects and is presented here as a case study. The relevant data obtained from the structure were used to predict its performance level for different time periods by combining two major effects of corrosion. Deformation due to bond-slip relationships and loss in cross-sectional areas of reinforcement bars were examined as a function of corrosion rate for five corrosion levels. Plastic hinges were defined as a consequence of corrosion effects, and they were used to perform nonlinear push-over analyses. Incremental dynamic analysis was then performed for 20 individual earthquake ground motion records to predict the structure’s ti...

CO2-full factorial optimization of an ultra-high performance concrete mix design

This article presents a factorial modelling, as well as an optimization, of the mix proportion of ultra-high performance concrete (UHPC) in terms of maximising the 28-day strength and minimising CO2 emissions. A full factorial design and desirability function optimization method were performed to find the best UHPC ingredient proportions. To improve the concrete properties, the concrete performance in terms of CO2 emissions and environment effects should be considered. Ultra-high performance with superior properties requires a large amount of cement, steel fibre and an admixture; however, from an environmental perspective, cement and admixtures and steel fibre are the important matter for global warming as cement production corresponds to 5% of all the CO2 emissions around the world. In addition, the 28-day compressive strength is one of the most important properties of concrete and is related to other mechanical properties; therefore, the 28-day compressive strength and carbon oxide emissions were selected as the responses to produce the green UHPC with high performance. The mix design parameters were the cement content (C), the steel fibre amount (F), the superplasticiser (SP), the silica fume amount (SF) and the water to cementitious ratio (W/C). The variables were compared by fine aggregate mass. The optimized ingredient mix designs are valid for the mixes with .18–.32 W/C ratio, .04–.08 steel fibre, .7–1.3 cement, .15–.30 silica fume, and .04–.08 superplasticiser by fine aggregate mass.

Effect of Density on Compressive Strength of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) Using Design of Experiment

This paper aims to model the effect of density in 7, 14, 28 days on compressive strength of Ultra High Performance Concrete (UHPC) in same compaction and curing conditions by Design of Experiments (DOE) methodology using vary range of 5 variables: Silica fume (SF), Steel Fiber, Cement 42.5, Superplasticizer (SP), and water cemetiotious ratio (w/c).The results shows the significance effect of density on compressive strength of UHPC in different days, The models are valid for the mixes made with 1.0 sand, 0.15-0.30 silica fume amount, 0.70-1.30 cement amount, 0.10- 0.20 steel fiber, 0.04- 0.08 superplasticizer (all values are by sand by weight mass) and 0.18- 0.32 water cementitious ratio.

Experimental Study on Engineering and Thermal Properties of Mortar and Plaster Produced With Pumice Aggregate

Now, it is widely accepted by civil engineers and architects that walls and masonry building units, which are made of pumice, can insulate buildings against both heat and sound, and also reduce the dead load of the building compared to traditional buildings. In this study, pumice was used as a fine aggregate in mortar and plaster instead of traditional crushed limestone sand. This study shows that the properties of pumice mortars indicate lower values compared to limestone mortars for workability durations, time of settings, and fresh and hardened unit weights. Other properties of pumice mortars indicate higher values compared to limestone mortars, such as water absorption, coefficient of capillary water absorption, drying shrinkage, flexural strength, and compressive strength. Also, wall systems made with pumice mortar and plaster show significant benefits in terms of thermal conductivity.

Effect of Corrosion Damage on the Performance Level of a 25-Year-Old Reinforced Concrete Building

Corrosion is a long-term process resulting in the deterioration of the reinforced concrete (RC) structures. Most of the structural problems observed under the impact of either earthquakes or service loads might occur due to corrosion. Therefore, prediction of the remaining service life of a corroding RC structure plays an important role to prevent serious premature damage. In this study, a corroded, 25-year-old high school building which has been demolished at an earlier time was analyzed as a function of corrosion rate. Bond-slip relationships were taken into account in nonlinear analyses as a function of corrosion rate for different time periods (i.e., non-corroded (t: 0), existing (t: 25) and 50 years after construction); and they were used to ensure the effect of time-dependent slip rotation on the global structural behaviour by modifying the target post-yield stiffness of each structural member. Nonlinear push-over analyses were performed by defining the time-dependent plastic hinge properties as a consequence of corrosion effects. In order to define the performance levels of three different time periods, nonlinear incremental dynamic analyses (IDA) were performed for 20 earthquake ground motion records as a function of corrosion rate. Results showed that bond-slip relationship between concrete and steel is very important in evaluating the non-linear behaviour of cor- roded RC structures.