Contribution Of Fly Ash Research Articles

Contribution of fly ash to mortar strength development under steam and internal curing

The purpose of this study is to quantitatively evaluate the effects of steam curing and internal curing on contribution of fly ash to strength development of mortar by using cementing efficiency factor (k-value) that represents strength development performance as a binder of fly ash. In addition, the pozzolanic reaction of fly ash was evaluated from the viewpoint of calcium hydroxide consumption by using thermogravimetry and differential thermal analysis as well as the degree of fly ash reaction by using selective dissolution method. The result indicated that steam curing improved early compressive strength and internal curing improved compressive strength and k-value at all ages. Also, a linearrelationship between the degree of fly ash reaction and the k-value was shown regardless of the age and the replacement ratio of fly ash.

Study on mechanical properties and air-void structure characteristics of hybrid fiber fly ash concrete under sulfate attack

Sulfate attack is one of the common durability problems of concrete. The concrete structure in saline soil is particularly susceptible to sulfate attack. The aim of this paper was to investigate the effect of fly ash on the mechanical properties and pore structure of fiber reinforced concrete under sulfate attack. The sulfate resistance of different content of fly ash (0%, 10%, 20%) at different sulfate attack ages (0 d, 30 d, 60 d, 90 d, 120 d, 150 d) was presented. By analyzing the variation of mass loss rate, ultrasonic wave velocity, relative compressive strength and relative splitting tensile strength, the mechanical properties of concrete under sulfate attack were studied. In addition, the air-void structure test was carried out to explore the pore structure characteristics of concrete. The test results suggested that the contribution of fly ash could improve the sulfate resistance of concrete. At the same sulfate attack age, compared with other contents, the hybrid fiber fly ash concrete with 10% fly ash could strong against sulfate attack. At the later stage of sulfate attack, the corrosion resistance of concrete weakened, the mass loss rate, wave velocity, relative compressive strength and relative splitting tensile strength were reduced, while the pore structure parameters showed that fly ash could fill large pores for reducing corrosion damage. Adding 10% fly ash refined pores and enhanced the strength of concrete. The generation of pores is main factor for the deterioration of concrete structure. The fractal dimension well expressed the changes of pores in concrete. Based on fractal dimension and fly ash content, the damage model was established, which could predict the damage deterioration of hybrid fiber fly ash concrete under sulfate attack.

Experimental Study of Effect of Fly Ash on Self-Compacting Rammed Earth Construction Stabilized with Cement-Based Composites

AbstractAs an environmentally friendly construction technique, modern rammed earth generally stabilized with portland cement has attracted growing interest recently. In this study, cement-based composites (CSCN) consisting of cement, sodium silicate, and composite promoter were used for substituting portland cement, and the effect of fly ash was investigated by unconfined compressive strength (UCS) test, thermogravimetric analysis (TG), X-ray diffraction (XRD), and scanning electron microscope (SEM). Based on the theory of pozzolanic and dispersing (P&D) effects, the contribution of fly ash was regarded as an addition of CSCN, and the quantitative analysis of P&D effects defined as P&D factors was evaluated by the clay-water/CSCN ratio hypothesis. It was found that the P&D factors for both compressive strength and secant modulus varied with CSCN content and curing age. The models of different curing ages for predicting the strength and modulus of specimens stabilized with CSCN and fly ash were developed f...

Influence of environment conditions on carbon emission of fly ash concrete

Adding fly ash in concrete can reduce CO2 emission and energy consumption. However, the increase of fly ash content always leads to reduction of concrete's compressive strength. Moreover, the contribution of fly ash to the compressive strength is also influenced by many environmental factors, such as curing temperature, humidity and time. In this study, the influences of curing humidity and temperature on the mechanical properties and total CO2 emission of fly ash concrete were investigated. The ratio of CO2 emission to the compressive strength of concrete was proposed to evaluate the contribution of fly ash to carbon emission. On this basis, it was found that CO2 emission of fly ash concrete was influenced by curing temperature and relative humidity greatly. Under different curing temperatures and relative humidities, the ratio of carbon emission to the compressive strength showed an obvious difference.

The contribution of fly ash toward indoor radon pollution from concrete

Owing to concerns about radon exposure, there is a need for understanding risk associated with fly ash in concrete. Monte Carlo simulations were applied, based on the radium specific activity of concrete constituents taken from the literature, to predict probabilities for the radium specific activity and radon exhalation rate. The model was then used to predict the indoor radon concentrations and effective annual doses from two different slab-on-grade concrete floors, one with and one without fly ash, in a typical single-family home in the United States. Due to uncertainty in the literature-reported values, a sensitivity analysis was conducted varying the emanation fraction of the fly ash concrete floors. The results show that concrete floors made without fly ash and a 5% emanation fraction, resulted in 90% of the simulated homes having an indoor radon concentration of less than or equal to 2.3 Bq m−3 and an associated annual dose of less than or equal to 54 μSv y−1. This annual dose represents 4% of the total annual background inhalation dose. A 25wt% fly ash concrete with an emanation fraction of 3% achieved the same exposure probability, but higher assumed emanation fractions raised the exposure probability. In general, the predicted radon exposure from fly ash concrete suggests minimal population health effects. But, given the serious health effects of radon exposure the influence of fly ash on the emanation fraction and radioactive pollution indoors deserves further exploration.

Fracture properties of high-performance concrete containing fly ash

A parametric experimental study has been conducted to investigate the effect of fly ash on the fracture properties of high-performance concrete (HPC), with four fly ash contents used. By means of three-point bending method, the fracture toughness, fracture energy, effective crack length, critical crack opening displacement, and maximum crack opening displacement of the specimen were measured, respectively. The results indicate that fly ash has great improvement on the fracture parameters, and these fracture parameters gradually increase when the content of fly ash increases from 10 per cent to 20 per cent. However, these fracture parameters begin to decrease after the fly ash content exceeds 20 per cent. Besides, as the fly ash content increases from 10 per cent to 20 per cent, the relational curves between the vertical load and the mid-span deflection ( PV– δ), crack mouth opening displacement ( PV– CMOD), and crack tip opening displacement ( PV– CTOD) become plumper and plumper, which indicates that the capability of HPC containing fly ash to resist crack propagation is becoming stronger and stronger, while the curves become shriveled after the fly ash content exceeds 20 per cent. The contribution of fly ash on the fracture properties of HPC containing fly ash seems to be performed only when the fly ash content does not exceed 20 per cent.

Combined effect of polypropylene fiber and silica fume on mechanical properties of concrete composite containing fly ash

A parametric experimental study has been conducted to investigate the combined effect of polypropylene fiber and silica fume on the mechanical properties (compressive strength, splitting tensile strength, and compressive modulus of elasticity) of concrete composite containing fly ash. Five different fiber volume fractions, four contents of fly ash, and four silica fume contents were used. The results indicate that the contribution of silica fume on the growth of compressive strength and splitting tensile strength is performed at the early curing period, and the contribution of fly ash on the growth of compressive strength and splitting tensile strength is performed at the later curing period, when the fly ash content is not beyond 20% and the silica fume content exceeding 3%. The addition of fly ash and silica fume greatly increases the compressive modulus of elasticity at 28 days curing. Though the addition of polypropylene fiber decreases the compressive strength of the concrete with fly ash and silica fume, the splitting tensile strength is improved and compressive modulus of elasticity is decreased effectively, which can decrease the rigidity and increase the ductility of the concrete composite containing fly ash and silica fume to protect the concrete from damages for large deformation.

Influence of Mixture Proportion and Curing Condition on Contribution of Fly Ash to Strength of Concrete

To investigate the strength efficiency of fly ash in concrete, the contribution of fly ash to strength, k value was calculated with the equation: the strength difference between fly ash concrete and control concrete with no fly ash due to the different fly ash content divides by the strength difference between both control concrete with no fly ash due to the different cement content which equals to the former different fly ash content. The k values were organized with fly ash specific surface area, concrete curing condition and age of specimens. Based on a large number of data collected from several proceedings and journals published in Japan during 1981 to 2003, the influences of fly ash property, mixture proportion and curing condition on k value were investigated. Within the range of study the following observations were made: (1) When fly ash concrete kept in moist curing, the k value of fly ash with specific surface area from 250 to 500 m2/kg is averagely 0.5 to 0.6 or higher at an age of 91 days and later, whereas that of fly ash with specific surface area from 150 to 250 m2/kg is around 0.4 to 0.5, and with some cases contributing little to the strength. (2) In the range of a portland cement content of 250 to 450 kg/m3, the strength contribution tends to increase as the cement content increases. (3) The contributions of fly ash to strength at 91 and 364 days are 1.44 to 1.97 times as large as those at 28 days, respectively, by standard curing, but conversely decrease to 0.75 to 0.79 times those at 28 days by air curing.