Investigation of Thermal Properties of Normal Weight Concrete for Different Strength Classes

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 908-914

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

Investigation of Thermal Properties of Normal

Weight Concrete for Different Strength Classes

Hamed Rezaei Talebi , Brit Anak Kayan , Iman Asadi , Zahiruddin Fitri Bin Abu Hassan

Department of Building Surveying, Faculty of Built Environment, University of Malaya, 50603 Kuala Lumpur, Malaysia

Center for Building, Construction & Tropical Architecture (BuCTA), Faculty of Built Environment, University of Malaya, 50603 Kuala Lumpur,

Malaysia

Received: 02/02/2020

Accepted: 01/06/2020

Published: 20/09/2020

Abstract

Concrete is a common construction material which its thermal properties influence on energy consumption of buildings,

significantly. The main aim of this study is to investigate the thermal properties of normal weight concrete for different strength classes

and the performance of normal weight concrete was measurement by studying the mechanical, physical and thermal properties. Also,

develop the correlations between thermal properties with mechanical and physical properties. The results showed that the thermal

properties of concrete would be changed based on its different strength classes. The results indicated that the thermal conductivity,

specific heat capacity and thermal diffusivity of normal weight concrete with a compressive strength in the range of 15 to 62 MPa are in

the range of 1.6 to 3.2 W/m.K, 0.92 to 1.16 kJ/kg.K and 0.69 to 1.34 (×10 m /s), respectively.

Keywords: Normal weight concrete, Thermal conductivity, Thermal diffusivity, Specific heat capacity

Introduction¹

According to available literature, the thermal conductivity of

aggregate used in concrete is in the range of 1.163 to 8.6

W/m.K [10]. However, the thermal conductivity of concrete

has been reported in the range of 0.2 to 3.3 W/m.K [11, 12, 13,

Concrete is a widely used construction material of the

world, that annual production of 5.0 billion cubic yards, the

concrete used amount is almost double of all other construction

industrial materials, the main detail mix proportions of concrete

with the water-cement ratio an important factor that effect on

the strength of concrete [1].The buildings are responsible for a

third of the total energy consumption and emit 30% of

greenhouse gases (GHGs) in the atmosphere [2]. The energy

needed for heating and cooling of structure also thermal

tranquility almost depend on the thermal properties of the

materials used in constructing a building [3]. The thermo-

physical properties of construction material play a significant

role in achieving the energy required for heating and cooling.

Compared to other building materials such as wood, steel,

and plastic, concrete is used twice as much in the construction

of buildings [4]. More than 10 billion tons of concrete is

produced each year [5] and it is expected that it reaches 18

billion tones by 2050 as demand for concrete continues to rise

4].

Using lightweight aggregates as a replacement normal

weight aggregates of concrete reduce the thermal conductivity

significantly.Replacement the fly ash can reduce the thermal

conductivity of concrete up to 80% [15]. In another study,

Huang et al. revealed that the thermal conductivity of concrete

with replacement fly ash is around 21% than a normal one [16].

A study reported the k-value of concrete is around 0.22 W/m.K

while tobacco waste added to mix [17]. Howlader et al.

reported that specific heat capacity of concrete containing burnt

clay brick-chips as aggregate is 13% greater than the concrete

having stone-chips, furthermore, the achieved results show that

the thermal diffusivity of concrete with burnt clay brick-chips

was 19% lower than stone-chips concrete [18].

Utilizing cementitious material as cement replacement can

change the thermal properties of concrete. Wongkeo et al.

reported that replacement cement by bottom ash (BA) up to

[6].

The thermal conductivity (k-value), specific heat capacity

c-value) and thermal diffusivity (α) represent the thermo-

0% can increase the k-value of autoclaved concrete around 5%

(

[19]. The concrete with thermal properties such as low thermal

physical properties of a material, the key thermal property

affecting the transfer of heat by conduction through concrete is

thermal conductivity, Asadi et al. reported that the thermal

conductivity for different types of concrete was 2.24 to 3.85

conductivity, low thermal diffusivity, and high specific heat

capacity is desirable for using insulation in buildings

construction [20].

Despite the available literature regarding the thermal

properties of concrete while cement or aggregate is replaced,

there is no information about the thermal properties of different

strength class of normal weight concrete. Also, the most

existing prediction models to predict thermal properties of

concrete is about predicting mostly thermal conductivity,

however, most of the proposed equations are valid for

lightweight concretes. The different grades of normal weight

concrete have various mix proportions and may differ in some

(

W/m.K) [7]. Conduction heat transfer in concrete occurs

through vibrations of the molecules and energy transport by

free electrons [8]. Thermal diffusivity indicates the speed of

heat transfer through concrete in transient heat transfer

conditions.

Concrete is a mix of cement, water, coarse aggregate, fine

aggregate and admixture in some cases. Changing in each

component will be changed the thermal properties of concrete,

around 60% of the concrete volume consists of aggregate [9].

Corresponding author: Brit Anak Kayan, University of Malaya, 50603 Kuala Lumpur, Malaysia. E-mail: brit284@um.edu.my.

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 908-914

ingredients. Therefore, it is expected that different grades of

normal weight concrete have different thermal properties.

This study aim is to consider thermal properties (thermal

conductivity, specific heat capacity, and thermal diffusivity) of

different grades of concrete with different mix proportions

while the type of coarse aggregate, fine aggregate, cement,

curing condition, and testing methods were the same. In

addition, due to the measuring of thermal properties of cement-

based materials require special equipment and test setups, this

study presents equations to predict the thermal properties based

on physical/mechanical properties.

they weighted, and the exact dimension was measured by

calipers.

2.3.3 Water absorption

The water absorption test values were measured according

to ASTM C642. The water absorption test was conducted on

100 mm cubic specimens. The saturated surface dry specimens

were dried in an oven at 105 ± 5 ℃ for 24 hrs. Dry weight (A)

was then recorded. Afterward, the specimens were immersed in

water at 20 ℃ until they achieved a constant weight (B). The

absorption at 30 min (initial absorption) and 72 hrs (final water

absorption), when the difference between two consecutive

weights was almost negligible, were calculated by the

following formula:

Experimental program

.1 Materials

In this study the ordinary Portland cement (OPC),

confirming the requirement of MS522 part 1:2003 with

compressive strengths of 36 MPa at 7days and 48 MPa at 28

days has been used. The 89 specific gravity and specific surface

Water absorption (%) = [(B−A)/A] × 100

(Eq. 1)

.3.4 Sorptivity

The sorptivity test values were measured by ASTM C1585.

area of the used OPC are 3.2 and 3510 cm /g, respectively

Table 1.

The Sorptivity test was carried out on the 100 mm cube

samples at the age of 28days. The weight of all samples was

measured before testing. The infused water in a tray in a depth

of 2mm of the tray. The samples put on rods with a 1 mm

diameter inside the tray. The weight of the samples was

measured after 5, 10, 30, 60, and 120 minutes. The sorptivity

was calculated by the following formula:

Table 1: The composition details of OPC (% by mass)

Chemical composition

Cao

OPC

63.40

19.80

5.10

3.10

2.50

2.40

1.00

0.19

1.80

SiO

푖

MgO

푆 = _√_푡

(Eq. 2)

K O

where S (g/mm /min¹^/²) is the sorptivity coefficient, i (g/mm²)

represents the cumulative amount of water absorbed per unit

cross-sectional, and t represents the time measured in minutes.

LOI

Also using from local mining sand with a saturated surface

dry (SSD) specific gravity of 2.55, fineness modulus of 2.8, and

water absorption of 1.5% was used in all mixtures. The water

used in all mixes was potable water from the pipeline in the lab.

The superplasticizer (SP) used is Sika Viscocrete-2192 from

Sika Company. The (SP) used is a modified polycarboxylate

type superplasticizer. Potable water, free from impurities and

chemical contaminants was used for all mixes.

.3.5 Thermal conductivity

Based on [21, 22] used from thermal conductivity were

determined by the KD2-Pro thermal conductivity analyzer in

compliance with the ASTM D 5334. In this study, three

cylindrical specimens (100mm * 200mm) at the age of 28 days

were selected to measure thermal conductivity at dry

conditions. The samples were oven-dried for 24 hours in the

degree of 100 ± 5 ˚C to remove all moisture. The k-value of

specimens was determined with KD2-PRO analyzer using TR1

needle. TR1 sensor with (2.4 mm in diameter and 100 mm in

length) is capable to measure thermal conductivity in the range

of 0.1 W/m.K to 4 W/m.K [23]. A pilot pin was inserted to the

uncured specimens to prepare the hole in the size of TR1

sensor. The 10 minutes reading of sensor and 15 minutes

interval, contribute to minimize errors derived from the large

diameter needle. The theory of KD2-PRO analyzer is based on

heating the needle for a time and monitoring the temperature

during heating and cooling. The influence of ambient

temperature on samples should be kept as minimum as possible

to achieve more accurate value while using KD2-PRO.

Therefore, the surface of specimens was wrapped by plastic

bags to minimize the effect of ambient temperature as can be

seen in Figure 1.

.2 Mixtures proportions

In this study, fourteen different normal concrete (NC) mixtures

were used. Variables include cement content, water to cement

ratio, fine and coarse aggregate contents to prepare different

resistive grades of NC without using cementitious materials.

The applied cement content ratio was in the range of 280 to 570

kg/m . To achieve low and high grades of concretes W/C ratio

was increased or superplasticizer used this ratio. The W/C ratio

varied between 0.34 and 0.94. The mix proportion of all NC are

given in Table 2.

.3 Testing methods

.3.1 Compressive strength

The compressive strength test was measured according to

the ASTM C39 at 7 and 28 days. A compressive strength test

was carried out on cubic specimens with 100 mm . The cubic

.3.6 Specific heat capacity

The specific heat capacity was measured based on the

specimens were removed from the molds after 1 day and were

cured in normal water till the test of 7 and 28 days.

method used by [24]. One foam ice box was prepared as a

calorimeter. The temperature changing of the 42 °C water was

.3.2 Oven dry density

Oven dry density test was cubic samples were dried at the

.8 °C in one hour, which demonstrated the box was well

insulated very well.

oven for 24 hours after curing. The samples were taken out

from the oven and wait to get cold for a few minutes. After that