Evaluating the Effect of Fly Ash on the Rheological and Mechanical Performance Self-Compacted Concrete

Jawad Ahmad^1*, M. Talha Ihsan², Aneel Manan¹, Osama Zaid¹, Rahat Ullah³ and Ghlum Abbas^4
*Correspondence: Jawad Ahmad, Department of Civil Engineering, Swedish College of Engineering and Technology, Wah Cantt, Pakistan, Tel: + 031492128912, Email:

Keywords

Sustainable concrete • Compressive strength • Split tensile strength • Self-consolidating concrete • Flowability • Passing and filling ability

Introduction

Self-Consolidating Concrete (SCC) is a special concrete which is highly flow able, non-segregating and by its own weight spread into place, completely fill the formwork even in the presence of dense reinforcement [1]. Self-compacting concrete (SCC) concept was proposed in 1986 by Hajime Okamura [2], however the prototype was first developed in Japan in 1988 by Ozawa [3].”

“Concrete is the highly used construction substance in the construction field because of its high stability & structural strength [4]. Construction related to sustainability has turned into crucial in the engineering sector & different beliefs have grown to minimize the effect of the environment of recent construction industries [5]. The cement business is fronting threats like cost raises in energy delivery, also to lessen CO₂ ejections & the delivery of unrefined materials in adequate quality [6]. Worldwide production of cement is increasing constantly from 1990 to 2050. This was expected because it is 2nd most consumed product on the earth after water. The industry is rapidly rising especially in developing countries like China & India that have a high need of cement for housing & infrastructure [7]. Last year, Pakistan produced 41.14 million tons of cement; according to International Cement Review [8]. The country's cement industry has already built capacity to produce 59.5 million tons in anticipation of future demand for housing and infrastructure [9].”

Keeping in view these concerns of environment, cost of materials for construction, shortage of raw materials and higher demand of energy, practice of utilizing alternate material is becoming a common concern of the globe [10]. In this research particularly focus to partially used fly ash instead of cement. FA is obtained from coal fired power plants by filtration processes. Chemical composition of FA the source from which it was collected [11]. It is suggested by researchers that consumption of supplementary cementitious materials in concrete helps to reduce the adverse environmental effects related to the manufacturing process of cement or concrete [12]. With utilization of these wastes as supplementary and replacement materials there is considerable energy conservation and reduction in the consumption of cement which aids in the reduction of release of carbon dioxide in the environment [13]. Moreover, there could be considerable improvement in the strength and durability properties with use of supplementary cementing materials in concrete [14]. It should be noted that the wide application of fly ashes from black coal and brown coal combustion in construction and building materials is mainly determined by the fineness, chemical and mineral composition, as well as pozzolanic activity-like cement. At the same time, fly ashes have a beneficial effect on the technical properties of concrete, improving its compressive and bending strengths, and frost resistance [15,16]. These factors make the production of ash concretes attractive to both producers and final consumers [17]. It has been reported that, the chemical properties and pozzolanic activity of fly ashes indicated the potential of this innovative additive [18].

The significant use of fly ash as a cement replacement for Concrete production opens the possibility for more sustainable concrete. The interests of developing more environment-friendly concretes where cement consumption is reduced using fly ash as cement replacement materials justifies the further exploration of the role this mineral material plays in concrete performance. The mechanical properties and durability with incorporation fly ash have been investigated by many researchers [19,20]. However, the use of fly ashes as a partial cement substitute increases water demand and reduces the workability and density of concrete mixes [21].

Fontes et al. [22] showed that cement mortars in which cement was replaced with FASS in an amount of 10% to 30% showed similar bending strength values to reference mortars. In addition, the partial replacement of cement with fly ash increased the porosity of concrete. It has been also demonstrated that the replacement of 20% of Portland cement by fly ash from sewage sludge may result in a reduction in compressive strength [23]. It is also observed that the compressive and bending strengths after 28 days of curing decreased in comparison to ordinary mortar [24].

In existing short literature review show that very limited research was carried on SCC with incorporation of FA. Furthermore, knowledge about the utilization of high-volume fly ash in self compacting concrete is still scarce. The successful utilization in prevailing environment will offer multiple benefits including cost effective solution to construction industry and reduced environmental and health issues and would have positive impact on the durability and mechanical performance of the system.”

Materials and Experimental Program

Cement

Ordinary Portland cement (OPC) type-1 in accordance to ASTM C150 [25] is used in this study. Its chemical and physical properties are displayed in Table 1.

Fine aggregate and coarse aggregate

Natural sand was used as a FA (fine aggregate) in all the mixes in SSD (saturated surface dry) condition, which was obtained from, Larencepur Wah Cantt Punjab Pakistan. Normal weight coarse aggregate (crush stone) in saturated dry condition (SSD) was obtained from Margallah Wah Cantt Punjab Pakistan. Nominal maximum size of coarse aggregate is 19. 5 mm. Different tests were performed on aggregate to evaluate its physical property as shown in Table 2.

Fly ash

Fly ash was obtained from ICI Pakistan- Soda Ash Plant, Khewra. Class-F fly ash having specific gravity 2.10 and dark brown color is used. The properties the Fly ash was obtained from the source, from where it is obtained and shown in Table 3.

Super plasticizer

Chemrite-530 used as super plasticizer because it is high range water reducing admixture and non-toxic and non-hazardous under relevant health and safety issue. The super plasticizer meets the requirements of EN 934-2 T 3.1/3 [17]. and ASTM C-494 Type F [26]. Typical properties of the super plasticizer are given as under Table 4.

Experimental program

To achieve the goal of project, a two stage experimental program was developed. In the first stage, trial mix was prepared in order to achieve the requirement of technical specification for SCC [1] as shown in Table 6. In the second stage, six mixes were prepared with varying percentages of FA (0%, 15%, 30%, 45% and 60% by weight of cement) to determine the effects FA on self-compacting concrete (SCC), which are based on the finding of the first stage. Typical acceptance criteria for Self-compacting Concrete define by technical specification for self-compacting concrete with a maximum aggregate size up to 20 mm are shown in Table 5.

Tests and size of specimen

Fresh properties of SCC such as Slump flow, Slump T50 Spread time, L-Box, V-funnel will be performed according to technical specification for SCC [1]. Cylinder of standard size (6 × 12 in) will be used to measure the compressive strength at as per ASTM C39/C39M [27]. Similar cylinders of standard size (6 × 12 in) will be cast and tested to find their tensile strength as per ASTM C496-71 [28]. Three specimens are tested for each test at 7,14 & 28 days and the mean value of the specimens is considered as strength.

Sample preparation method

ASTM C-31 [29] method was followed for the preparation of the specimens and compaction was done manually by Roding in three layers having 25 blows per layer. Six mixes are prepared with varying dosage of FA. Details of the mixes are provided in the following Table 6. Before the mixing process was started, the required quantity of material was weighed by method of weighing. Speed of mixer was kept 35 rev/min for mixing of materials. First, coarse aggregate was added to the mixer & then fine aggregate, both materials were dry mixed then necessary quantity of cement and water were added with time and mixing was done about 8 minutes for all mixes.

Conclusions

In this research fly ash was used as a binding material in proportion of 0%, 15%, 30%, 45%, 60% by weight cement. Based on experimental work following conclusion has been drawn.

• Fresh properties of SCC such as flowability, passing and filling ability decreased as the percentages of fly ash (FA) increased. It is due to the physical properties of fly ash which is porous and tends to absorb more water However up to 45% of fly ash (FA) by weight of cement will fall within the limits define by technical specification for SCC and have good flowability, passing filling ability.

• At 7 days curing, strength (compressive and split tensile strength) decrease as the percentages of fly ash (FA) increased as compare to blank mix. However, at 28- and 56-days curing, strength (compressive and split tensile strength) increase as the percentages of fly ash (FA) increased up to 45% by weight of cement and then decreased as compare to blank mix. It is due to pozzolanic reaction, which forms secondary C-S-H gel allowing concrete to gain more strength over the time. However, at higher dosage (FA- 60%) compaction process become more difficult due lack of flowability, leading to porous concrete which results to decreased ultimate strength of SCC.

• Therefore, it is advisable to used fly ash (FA) up to 45% by weight of cement to obtain maximum benefits by considering workability and mechanical performance of SCC.

Conflict of Interest

All authors declare no conflicts of interest in this paper.

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