Characterization of Thermo-Physical Properties of Cement-Based Blocks of Varied Sand Types Using Cost-Effective Enhancement Approach

The dominant property of building envelope fabric which contributes sig-nificantly to minimize electricity utilization in building is the thermo-physical properties. There is inadequate literature on representative practical data of thermo-physical properties of the dominant building envelope components in Ghana. This study aims to use cost-effective approach to characterize the thermo-physical properties of only cement-based mortar and concrete blocks used in Ghana for building components specifically wall design. Mixed methods research design was employed to achieving the aim. A questionnaire survey was used among sampled building fabric components manufacturers to pick representative data on thermos-physical properties of their mortar and concrete blocks. Also, an experimental procedure employing a transient technique with a TCi Thermal Analyser was used to determine the thermo-physical properties of selected mortar and concrete blocks from Ghana in addition to designed parametric mortar and concrete blocks with varied ratios obtained from the survey were undertaken at University of Nottingham. From the study, a trend of decreasing thermal conductivity and thermal effusivity with corresponding decreasing sand content was observed with all the different sand types. The thermal conductivities of both mortar and concrete parametric blocks meet the range of expected standard values outlined in Chattered Institute of Building Services Engineers (CIBSE) Guide A. The major limitation of the work is the dimension of the sample size; which is not inconsistent with standard block size due to the experimental setup used. It is expected that, the characterization of

in Ghana. This study aims to use cost-effective approach to characterize the thermo-physical properties of only cement-based mortar and concrete blocks used in Ghana for building components specifically wall design. Mixed methods research design was employed to achieving the aim. A questionnaire survey was used among sampled building fabric components manufacturers to pick representative data on thermos-physical properties of their mortar and concrete blocks. Also, an experimental procedure employing a transient technique with a TCi Thermal Analyser was used to determine the thermo-physical properties of selected mortar and concrete blocks from Ghana in addition to designed parametric mortar and concrete blocks with varied ratios obtained from the survey were undertaken at University of Nottingham. From the study, a trend of decreasing thermal conductivity and thermal effusivity with corresponding decreasing sand content was observed with all the different sand types. The thermal conductivities of both mortar and concrete parametric blocks meet the range of expected standard values outlined in Chattered Institute of Building Services Engineers (CIBSE) Guide A. The major limitation of the work is the dimension of the sample size; which is not inconsistent with standard block size due to the experimental setup used. It is expected that, the characterization of the predominant cement-based building fabrics components will contribute to improved building performance analysis with significant savings in electricity utilization for space cooling.

Introduction
In recent years, attention has been paid to reducing energy consumption in buildings towards achieving a Net Zero Energy Building (NZEB). The building sector has been the second largest energy consuming sector after transportation with 28% of final global energy consumption [1] [2] [3] [4] thus presenting a significant potential for energy savings and greenhouse gas emissions reduction. Adoption of high-performing building envelope is regarded as a prerequisite to reduce energy consumption of buildings because it is the main barrier of protection from heat transfer [5]. Studies by [6] [7] established that a building's cooling load, and by extension the energy consumption, correlates with heat transfer through the building envelope [6]. Therefore, minimizing heat transfer through building envelope is crucial for reducing cooling load. The selection of building fabrics should be carefully considered to enhance their potential in minimizing heat and moisture transfer through building components for improved performance, and consequently, the energy and indoor environmental quality [8]- [13].
There are other measures that enhance building performance such as controlling solar gain through window, thermostat set point, building control systems, programmable thermostat, and architectural design parameters such as building form, window properties, thermal insulation level. Techniques such as application of passive cooling techniques, high-reflectivity coating on building walls, air tightness, phase change materials, reduction of u-values, daylighting harvesting all contributed to efficient energy use and improved indoor environmental quality in buildings [14]- [20].
In spite of the above techniques, [21] asserts that, Ghana experiences high cooling load in air-conditioned buildings and thermal discomfort in naturally ventilated buildings as a result of low levels of integration of high-performance technologies in buildings, and this has been attributed largely to their high cost.
There are a number of indigenous building envelope fabric available in the developing world, including sand, clay, laterite, wood, bamboo, stones, and cement-based fabric [22]. Among the indigenous fabric, a number of studies have been carried out on clay, the most abundant material, to valorise its use for thermal insulation applications [23]. The physio-chemical properties of soils can be altered or modified by adding stabilizers (admixtures) such as cement and lime, a process termed as soil-stabilization. However, cement-based materials such as mortar and concrete blocks have remained the most predominant material for use as building envelope materials in Ghana [21] [22]. The Cabinet of Ghana passed a bill in 2010 that at least 60% of the content used in construction of public buildings to be made up of indigenous raw materials.

E. A. Adjei et al.
A gap exists in literature on practical data of thermo-physical properties of materials used as envelope in buildings in the Sub-Saharan countries [10]. Several factors such as surface area, thickness, thermal transmittance, among others influences heat transfer into building envelope. The unavailability of thermo-physical properties of the most commonly used building envelope fabric leads to either an overestimation or underestimation of cooling load in the sizing of HVAC system for buildings. In instances of overestimation, there is wastage in the energy consumption for space conditioning. On the other hand, the underestima- Thermo-physical properties of permeable materials are affected by several factors, for example thermal contacting agent, porosity, compactness among others [8] [18]. Blocks with relatively lower cement content turn to have larger size pores and blocks with higher cement content turn to have large number of smaller pores.
[26] study shows the variation of total pore volume under different bulk densities of the same standard brick materials and was found that, denser materials were found to have lower total pore volume, thereby resulting in high conductive heat transfer.
In the context of the above, the aim of this study was to characterize the thermo-physical properties of mortar and concrete blocks made from the available types of sand in Ghana using cost-effective enhancement approach. The study sought to: 1) explore the thermo-physical properties of mortar and concrete blocks using a questionnaire survey among selected building fabric manufacturers in Ghana; 2) To compare the thermo-physical properties of mortar and concrete blocks selected from building fabric manufacturers with representative values from the CIBSE Guide values; and 3) to determine the thermo-physical properties of the parametric mortar and concrete blocks made from various sand types based on the dominant mixing ratio identified from the survey to determine the best sand type and mixing ratio for lower thermo-physical properties.
It is expected that, the characterization of the mortar and concrete blocks, being the predominant building envelope fabrics, will contribute to improve building thermal performance analysis, with significant savings in energy consumption for space cooling.

Thermo-Physical Test Method
Several thermos-physical test methods exist in both scientific and technical journals research, among them are steady [27] [28] and transient state techniques [29]. Steady state technique offer simple measurements methods without any complex means of analysis, conversely, it has relatively long time in reaching DOI: 10

Methodology
The procedures involved in the questionnaire survey among a sampled building fabric manufacturer and the experimental setup to determine the thermo-physical properties are explained in this section.

Questionnaire Survey
The   deviation of 7.1% and 0.7% respectively. This implied that, the error arising from the measurement of the set-up is minor and hence negligible. The procedures employed in the preparation of manufacturers samples and parametric mortar and concrete blocks for testing are explained in the following sections.

Preparation of Selected Mortar and Concrete Blocks for Testing
Due to the significant 80% of building manufacturers response in agreement of implementing thermal building regulations, randomly selected building fabrics were sent for experimental investigations to ascertain typical properties indicated in the survey. A series of tasks involving four stages were carried out prior to the main thermo-physical test measurement: 1) measurement of weight and dimensions of samples; 2) division of each samples into at least 6 parts, labelled with anonymous names and for a radioactive test by Ghana Atomic Energy for customs clearance for shipping to the UK as shown in Figure 3(v); 3) moisture control of the specimen in UK were carried out as a result of moisture transfer and temperature variation between Ghana and UK. The experiments blocks were at ambient temperature of 25˚C with a moisture content of 10%; and 4) reduction of sizes and surface finishing of specimen as represented in Figure 3.

Preparation of Parametric Mortar and Concrete Blocks for Testing
The following series of tasks were employed to develop parametric mortar and concrete blocks: 1) Specification of parametric mortar and concrete blocks; and 2) Design and Casting of samples.  The sand types were i) washed sand; ii) builders' sand; and iii) mixed washed and builders' sand, thus resulting in five ratios for each types of sand, making a total of 15 parametric blocks for each of mortar and concrete. The builder's sand was selected in accordance with [31] standards whiles the washed sand was selected in accordance with [32] standards.

1) Specification of parametric mortar and concrete blocks
Ratios of parametric mortar blocks and concrete blocks are presented below: Various (5)

2) Design and Casting of samples
The preparation of specimen moulds, casting of the concrete samples and compaction were guided by [33] [34]. Wooden boxes of unit size of 50 mm × 50 mm × 50 mm was used for casting the parametric mortar blocks and the concrete blocks (Figure 4(a)). Mortar and concrete blocks are dry after 28 days of ambient drying period per specifications of [35] and was further tested using simple moisture experiment, that is, three days continuous weighing of samples to ascertain there were no more variation in weight. Figure 4(b) presents samples of the tested parametric blocks.

Results and Discussions
The discussion of the results has been categorized into three areas: Representative Thermo-physical properties from survey; Thermo-physical properties of selected existing building fabrics in Ghana; and Thermo-physical properties of parametric mortar and concrete blocks using varying mixing design ratios from survey and varying sand types.

Representative Thermo-Physical Properties from Survey
The representative thermal conductivity of the selected mortar block and concrete block samples are presented in Figure 5 and   As seen in Figure 5, 30% participants indicated thermal conductivity of mortar block in the range of 0.5 -0.75 W/mK, and 19% indicated that they do not know the thermal conductivity. With respect to the concrete block samples, respondents indicated varied thermal conductivites from 0.03 -1.6 W/mK in Figure 6.
33% of respondents indicated that they do not know the thermal conductivity for concrete blocks.

Thermo-Physical Properties of Selected Existing Building Fabrics in Ghana
It was assumed that, for the same sand, mixing design ratios, as well as the use of these standards [33] [34] [35] irrespective of the dimension of the block's dimension, the experimental thermal conductivity remains the same.
The thermal conductivity of mortar block and concrete block from the selected building fabric manufacturers in Ghana are compared with the CIBSE Guide A range of values in Figure 7 and Figure 8. With respect to the survey data in Figure 5, in Figure 6 shows that the indicated thermal conductivity for concrete blocks fabric is in the same range as that of the experimental results from sample concrete blocks from Ghana in Figure 8, that is, 0.3 -0.76 W/mK. The thermal effusivity of mortar block and concrete block samples are presented in Figure 9 and Figure 10. Thermal effusivity values varied from 615 Ws 1/2 /m 2 K to 1060 Ws 1/2 /m 2 K for the specimens collected from the companies. A trend of decreasing thermal effusivity with decreasing thermal conductivity was observed. This implies that thermal contacting agent used in Polymer test method for thermal conductivity measurements has no effect on thermo-physical properties.

Thermo-Physical Properties of Parametric Mortar and Concrete Blocks
The thermal conductivity and thermal effusivity of the parametric mortar and concrete blocks determined by TCi Thermal Conductivity Analyzer based on modified transient plane source are presented in this section.

Thermal Conductivity
The effect of the various ratios of the parametric mortar and concrete blocks on thermal conductivity is presented in Figure 11 and Figure  (with 1 part of cement to 1 part of gravels and 4 part of sand) had thermal conductivity of 0.24 W/mK. There is no appreciable variation in thermal conductivity among the mixes for the various sand types. This implies that the differences in thermal conductivity results mainly from the varied ratios of cement, gravels and sand and for a given sand type.
From the assumption above, and using a typical standard block dimension with the obtained cost-effective thermal conductivity, the thermal transmittance of a single leaf wall use in Ghana can be estimated using Equation (1)  (1) where d = thickness (depth) of material layer, λ = thermal conductivity of the material Thermal Transmittance where Rt is the total thermal resistance. The summarized U-value of a typical wall at Ghana is shown in Table 1.

Thermal Effusivity
A trend of decreasing thermal effusivity with corresponding decrease of sand content for all the mixing ratio, T 1 to T 5 (mortar) and T 11 to T 55 (concrete) for all the sand types. The thermal effusivity of parametric mortar blocks lie in the range of 460 Ws 1/2 /m 2 K to 890Ws 1/2 /m 2 K for the different mixing ratios, with the lowest being achieved by the mixed builder's and washed sand blocks as presented in Figure 13. Among the builder's sand and washed sand blocks, the lowest thermal effusivity were achieved by the ratios with 1 part of cement to 2 parts of sand as 610 Ws 1/2 /m 2 K (MbsT 5 ) and 605 Ws 1/2 /m 2 K (MbsT 5 ) for builder's sand and washed sand types respectively. For each sand type, there was a general decrease in thermal effusivity form the T 1 ratio to the T 5 ratio with a decrease of about 27% (builder's), 32% (washed) and 49% (combined). The parametric concrete blocks also achieved decreasing thermal effusivity among various ratios from T 11 to T 55 the three types of sand of about 18% (builder's), 13% (washed) and 9% (combined) as presented in Figure 14. However, the T 11 ratio achieved relatively lower thermal effusivity that the corresponding mortar blocks and a higher thermal effusivity than the mortar blocks for the T 55 ratios.
This result shows a linear relationship between thermal conductivity and thermal effusivity as the thermal effusivity increases with decreasing thermal conductivity. This result is in agreement with [39]. Moreover, the parametric concrete blocks achieved a relatively narrow drop of both thermal conductivity and thermal effusivity among the ratios for all the sand types tested.

Conclusions and Recommendations
This paper presents the results of an experimental study characterizing the thermo-physical properties of cement-based building fabrics in Ghana using a cost-effective enhancement approach. The thermo-physical properties of analyzed building fabric samples selected from manufacturing companies and that of parametric blocks were found to meet the range of standards outlined in CIBSE Guide A. This established thermo-physical properties of the varied ratios of cement-based blocks (mortar and concrete) implies that simulation works involved in thermal building performance analysis in Ghana, can be accurately done. As a recommendation, the incorporation of technology and additives could be explored in the design and manufacturing of building fabrics to achieve the thermal transmittance specified for building envelopes in building regulations. Moreover, there is the need for studies to establish other properties such as density of mortar and concrete blocks made from the locally available materials.