Durability Properties of concrete incorporating calcined Phyllite

The environmental and economic concern is the biggest challenge that concrete industry is facing today. Advancement in utilization of wastes in concrete as a mixture reduces usage of natural resources. Phyllite is a kind of foliated metamorphic rock generates during underground mining .Phyllite was calcined at 850 to 900C in furnace and ground in ball mill. In this study, cement was partially replaced by weight with calcined phyllite to make M30 grade of concrete with 0% (Control mix), 2%, 4%, 6%, 8%, & 10%, (which are designated as M1, M2, M3, M4, M5 and M6). The laboratory tests such as slump value, compressive strength, flexural strength, water absorption, chloride ion penetration and durability in acidic and basic medium were conducted on the phyllite concrete and results are compared with the control mix. Through results it is concluded that cement can be replaced in concrete at the tune of 8% with Calcine Phyllite (CP) without affecting the strength and durability. The aim of the experiment is to find the maximum content of mines calcined Phyllite that can be used as a partial replacement of cement without compromising the quality on any of the characteristics of concrete.


Introduction
Around the world, calcined phyllite (CP) is an active pozzolanic admixtures which is used for reducing the cement content in mortar and concrete production. The raw phyllite was procured from the lime stone mine situated at village Basantgarh, Rajasthan (India) which is created from slate which primarily compose of Quartz, Hematite, Muscovite, Albite, Anorthite, Microcline.
Adom-Asamoah & Afrifa used phyllite coarse aggregate in concrete which showed 15-20% lower compressive and flexural strength as compared to conventional granite aggregate concrete [1].
Various studies indicated reduced quality of mortar due to incorporation of phyllite, however phyllite clay can be used due to the saving in cost and low energy consumption in production of mortar [2,3,4]. The ductility, flexural strength and shear strength of phyllite RC beams got decreased as compared to conventional aggregate beams [5]. Phyllite is found suitable to be used as sealing liner in irrigation ponds and as core material of small earth-zoned dams [6]. Schulze & Rickert recommended based on their study that appropriately calcined clay could be used as a supplementary cementitious material [7].
No research work has been found so far to study the effect of calcined phyllite on the properties of concrete. Looking to the availability of phyllite in abundance, the main objectives of the present research is to investigate its effect on strength and durability of concrete by the partial replacement of cement. Therefore, it is a novel work in the direction of utilization of phyllite waste material in the manufacture of concrete by the partial replacement of cement.

Materials
Ordinary Portland cement 43 grade conforming to IS: 269:2015 was used in the study. Banas river sand was used as fine aggregate. Coarse aggregates (20 mm and 10 mm size) were procured from locally available commercial quarry. The phyllite was procured from the limestone mine situated at village Basantgarh, Rajasthan (India). Figure -1 shows the phyllite waste lying at mine site. The phyllite was procured from the lime stone mine situated at village Basantgarh, Rajasthan (India)which is created from slate, that is further metamorphosed and very fine grained white mica achieved a preferred orientation. Calcined Phyllite and Normal Phyllite are shown in

2.2.1Determination of Compressive strength test
Compressive strength was conducted on cube specimens of 150 mm size at an age of 7, 28, and 56 days. Fifty-Four cubes were tested for CST as taking avg. of three cubes for each design mix for CST of all mixes to find the average compressive strength.

Determination of Flexural strength test
Flexural strength was prepared of 36 beam specimens of size 500 mm×100mm×100mm. Flexural strength of three specimens for each design mix and tested at the age of 7 and 28 days. Freshly mixed concrete was filled in three layers and each layer was compacted manually by 150 strokes using a 25mm diameter steel tamping rod. The hardened beam specimens were tested using automatic universal testing machine & average of three specimens was reported flexural strength of that mix. Flexural strength test was conducted as per IS 516 -1959.

Determination of Water absorption test
Water absorption is measured by measuring the increase in mass as a percentage of dry mass. internal water absorption were investigated. Water absorption is measured by measuring the increase in mass as a percentage of dry mass as per Indian standard.

Determination of Rapid Chloride Ion Penetration Test
Rapid chloride ion penetration test was performed at 28days and 90 days' concrete as per recommendations of ASTM C 1202. The amount of electrical current passed through 50 mm thick slices of 100 mm nominal diameter cores during a 6-hour period is monitor in the test. A potential difference of 60 volts direct current is maintained across the ends of the specimen, one of which is immersed in a sodium chloride solution, the other in a sodium hydroxide solution. The total charge passed, in coulombs, has been found to be related with the resistance of the concrete specimen to chloride ion penetration. Durability Test of concrete structures made up of blank and structures with 8% replaced Calcined phyllite were test for 28 days in harsh environment of acid and alkaline nature. Cubes were cured in normal water, NaCl solution and 1:2 H2SO4 acid solution to analyze and conclude concrete properties.

Determination of Durability Test in Acid Medium
Durability test both in acid & basic medium was conducted to address the issue of corrosion in reinforcement of RC structures and results were compared with the results of neutral environment specimens. This test was conducted only on the concrete mixes M1 (control mix) and M5 (8% CP concrete).

Concrete mix design and workability
In

Results and discussion
The phyllite is thermally treated for calcinations in a muffle furnace at 850°C for two hours to ensure transformation to amorphous state of its minerals, it was observed that the Lime Reactivity   Calcined phyllite (%) 7 days 28 days M1 at the age of 7 and 28 days, respectively. This proves that concrete mix with 8% calcined phyllite is dense in nature and restricts capillary action to certain extent.
The resistance to chloride ion penetration at 28 days and 90 days age of concrete for mixes M1 and M5 measured in terms of electric current passed through the specimens in coulombs are shown in Figure 7. The graph shows that total charge passed decreases from 3895 to 453 coulombs in the mixes M1 to M5 at 28 days age of concrete. Also at 90 days' age of concrete, the value decreases from 2411 to 389 coulomb. The mixes with 8% CP showed lower values of charge passed as compared to corresponding control mix (0% CP) at both ages (28 and 90 days) indicating higher resistance to chloride ion penetration. As per ASTM C 1202, coulomb values in between 100-1000 indicate very low penetrability concrete, hence the concrete with optimal CP content is less permeable and can be used for structural purpose as well. The test results are shown in Figure 8. The test results of durability show that after curing in acidic medium for 28days M1 has decreased in strength by 11.24% whereas concrete with 8% CP has decreased just 5%. Also in alkaline medium for 28days M1 has decreased in strength by 23.46% whereas concrete with 8% CP has decreased just 11.65%.

Conclusions
The key findings based on this experimental investigation are as follows: 1. The compressive strength and flexural strength of phyllite concrete increased significantly up to 8% substitution of cement by CP at all ages, however rate of increase in 7-day strength was more as compared to other aged concrete.
2. Chloride-ion penetration test results showed lower values of charge passed in the concrete mix with 8% CP as compared to corresponding control mixes (0% CP) at both ages (28 and 90 days), indicating higher resistance to chloride ion penetration in CP concrete.
3. Durability test in acidic and basic medium showed better durability of 8% CP concrete as compared to control mix. Based on above test results, it is recommended to use calcined phyllite in concrete by substituting cement in the tune of 8%. The bulk utilization of CP as partial replacement of cement may contribute to the sustainable development. It will conserve the limestone resources used in the manufacture of cement and will also help in reducing the carbon footprint associated with the cement industry.