**3. Method**

#### **3.1 Materials and characterizations**

In the research work, PPC, river sand, stone aggregate of 10 mm down size, potable quality water and coal ash were used. For material characterization, quantitative chemical analysis (for cement, sand, fly ash and bottom ash), X-Ray Diffractogram (XRD) (for cement, sand, fly ash and bottom ash), sieve analysis (for sand, bottom ash and stone aggregate), particle size analysis (for fly ash), density test (for cement, sand, fly ash, bottom ash and aggregate), surface area determination (cement, fly ash and bottom ash) and Finite Element Scanning Electron Microscopy (FESEM) (for sand, fly ash and bottom ash) were carried out as per standard testing protocol. Chemical analysis results are tabulated and XRD and FESEM images (of fly ash and bottom ash) are shown below (**Figures 1**–**4** and **Table 1**):

Grading curve obtained by sieve analysis for bottom ash sample and particle size curve of fly ash sample are shown below (**Figures 5** and **6**):

**Figure 1.** *XRD of fly ash sample.*

**Figure 2.** *XRD of bottom ash sample.*

#### **3.2 Experimental programme**

The main objective of the experimental investigation is to ascertain the physical strength of the Concrete and Mortar mixes and finding out the thermal conductivity value of such mixes. The different mixes were designed with replacement of natural mineral by Coal ash and the changes thereof with respect to the physical and thermal properties.

Concrete mix design on the basis of basic ingredient material properties and fixing of proportions as per IS 456: 2000 [30], IS 10262: 2009 [31] and SP 23: 1982 [32] code provisions. Mortar mix selection as per relevant IS 2250: 1981 [11] code provisions.

**Figure 3.** *FESEM of flyash at 10000X.*

**Figure 4.** *FESEM of bottom ash at 20000X.*

Universal testing machine for compressive strength determination and apparent porosity and bulk density test apparatus for concrete and mortar samples were utilized. For thermal conductivity determination of concrete and mortar samples, hot disk TPS 2500S instrument (working on Transient Plane Source method by following ISO 22007-2) was used and for overall heat transfer coefficient determination (U-value), guarded hot box method was adopted. Altogether around 200 samples were prepared and tested. Some of the concrete and mortar mixes are tabulated as below (**Tables 2**–**5**):
