PSI - Issue 14

D. Anupama Krishna et al. / Procedia Structural Integrity 14 (2019) 384–394 A. Krishna et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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2. Experimental studies

The experimental methodology consists of mix proportioning, casting of specimens, exposing the specimens to elevated temperature and testing. The methodology has been briefly described below.

2.1. Materials and Mix proportion

In this investigation, ordinary Portland cement (OPC 53) conforming to IS 12269 -2013 was used. The sieve analysis forcoarse aggregate and fine aggregate was carried out. The former conforms to Zone II of Table 2 in IS 383-1970 and the latter conforms to Table 3 of IS 383.Fresh concrete testing was carried out according to IS 8142 1976.The mix design for M20 grade of concrete was carried out according to IS 10262-2009, with a slump value of 60mm, exposed to severe condition and with a target mean strength of 28.25 MPa. The final mix proportions obtained is listed in Table 1. The test strength obtained was 32.4 MPa.

Table 1.Mix proportion for the concrete Property

Mix

Cement content (Kg/m 3 )

364.5

Fine aggregate (Kg/m 3 ) Coarse aggregate (Kg/m 3 )( max. 20 mm.size) Water ( l )

546.75 1093.5 164

2.2. Casting and Curing

Standard size cubes (150mm x 150mm) and cylinders (150mm diameter and 300 mm height) were casted for testing the residual compressive strength, tensile strength and stress – strain relationship of concrete after exposure to elevated temperature. The specimens were cured for 28 days and air dried in the laboratory for 24 hrs. and oven dried at 105 o C for 24 hrs. Finally the specimens were subjected to a temperature range from 100 o C to 1000 o C.The specimens were then air cooled and tested. The details of the specimens with type of test, designation, number of specimens tested, cooling method and fire duration are listed in Table 2.

Table 2.Specimen description for residual Strength test on concrete Specimen Test on concrete

Fire duration ( t )

Designation

Number

Cooling method

Cubes

Compressive Strength

A1 B1 B2 B3

30 30 30 30

Air cooling Air cooling Air Cooling Air Cooling

1hr 1hr 1hr 1hr

Cylinders Cylinders Cylinders

Tensile Strength

Stress-Strain

Compressive Modulus of Elasticity

2.3. Fire exposure The specimens were exposed to a temperature as per the fire curve in Fig.1 [CNS (2005), ISO (1999)]. After the exposure the specimens were allowed to cool. For testing the residual strength property of concrete two methods for cooling were adopted, (1) Through air cooling by exposing the hot specimens to room temperature and (2) through water cooling by quenching the specimens in water just after the exposure to elevated temperature.