The SCG is obtained from Starbucks Coffee located in Kuantan. When collected directly from the coffee shops, the SCG is usually stuck to the filter paper in the tamp used to produce the coffee concentrate and other smaller rubbish pieces. Therefore, the unwanted materials are removed, and the SCG is oven-dried for 24 hours at 100 °C. The SCG was then sieved using a 600 µm pan and weighted as shown in Fig. (1). The nominal size of the coffee grounds used in this study is between 250 µm and 550 µm, similar to Kua et al. [19]. The Ordinary Portland Cement (OPC) is a key material in producing concrete or mortar. Due to its reaction with water, the hydration process results in it being capable of bonding the materials in a compact, rigid and robust form factor. In this study, the Orang Kuat Portland Cement brand from YTL Corporation was used, and it was classified as Type I cement according to MS EN 197 Part 1 [20]. The chemical composition and physical properties of Orang Kuat Portland Cement are tabulated in Table 1. This study used river sand, and the particle size passed 4.75 mm. The physical properties of sand were tested based on ASTM C778 [21] and ASTM C128 [22], tabulated in Table 2. The ratio of cement (1): fine aggregate (2.75): water (0.6) used to produce the N-type concrete mortar, which is recommended for masonry products, as stated in ASTM C1329-05 [23].

Fig. (1). Sieving and weighting process of SCG.

The percentages of SCG incorporated into the mortar mix vary from 0%, 0.5%, 0.75%, 1%, 2%, 3% and 4% respectively. The different percentages of incorporations added to the mortar were based on the weight of raw materials used to produce the mortar. For example, the total weight of raw materials is 4.35 kg. Therefore, 21.75 g of SCG was added to the 5% sample mix. A similar approach has been implemented by Sena da Fonseca et al. [12], where different percentages of SCG were used as an additive. The different percentages of SCG were added to the mix by material weight. The full list of samples is tabulated in Table 3. The sample of the concrete mortar cubes produced was cast in molds (50 mm x 50 mm x 50 mm) based on British Standard (BS 1881: Part 108) [25].

The flow table test is carried out to determine the optimum percentage of SCG for the same water-cement ratio. It involves measuring the mean diameter of the slump or “cake” that spreads out from the fresh mortar. The flow table cone's internal surface is cleaned and must be free of excess moisture before conducting the test. Then, a cone, a non-absorbent, smooth, horizontal, and rigid surface free from vibrations or shock from the nearby surroundings, was placed on the flow table. The fresh mortar was then layered in 3 different layers, with each layer being tamped for 25 strokes with a tamping rod. The flow table cone was removed carefully, and the wheel was spun to raise the table and drop 25 times. The flow of the mortar was then observed, and the mean diameter of the mortar spread was recorded, as stated in ASTM C1437-15 [26]. The percentage of flow value is calculated using Eq. (1).

(1)

Where:

FV = Flow value (%)

D_r = Average diameter of mortar

D_m = Base diameter of mold

The compressive strength test of the water-cured sample is conducted immediately after the removal of specimens from the curing tank. The standard used in this study is based on BS 1881: Part 116:1983 [27]. The sample was subjected to compression loads and tested until failure. The maximum load achieved from this test was taken as the ultimate load for future strength calculation. The test was conducted by first measuring the dimensions and weight of the specimen. These readings were recorded for the analysis. The specimen was tested at 7, 28 and 45 days. Before placing the sample in the compression machine, the upper and lower bearing plates of the machine were wiped clean along with the faces of the sample. Then, the samples were placed at the center of the bearing plates, and the machine was calibrated before beginning the test. The load shall be applied consistently, without shock, until failure occurs. All the readings, such as the maximum load, type of failure, and crack pattern, were recorded.

The dry density of hardened mortar was calculated using Eq. (2) by BS EN 1015-10 [28]. 50 mm mortar cubes were molded and allowed to air cure for 28 days at room temperature (28 °C +/- 2 °C) with an average relative humidity of around 85%. In this study, air curing was used to simulate the realistic scenario. The specimens were then placed in the oven at 60 °C for 24 hours. Then, the cubes were weighted for the dry masses to determine the dry densities.

(2)

Where:

DD = Dry density (kg/m³)

Dm = Dry mass measured after oven-dry (kg)

Vc = Volume of mould (m³)

The water absorption test was conducted following the standard by BS 1881-122:1983 [29], and the test's purpose was to determine the quantity of water absorbed under specific conditions. The test has been carried out by measuring the quantity of water a specimen absorbs over a specific period. The specimens used in this test have completed the 28 days of curing. After the curing period, the specimens were oven-dried for 72 hours and kept in an air-tight container for 24 hours. The specimen was weighed and cured in water for 30 minutes and 24 hours. After each interval, the specimen was weighed again for the final weight. The percentage of water absorption is calculated using Eq. (3).

(3)

Where:

WA = Water absorption (%)

W_i = Initial weight of the concrete cubes in grams

W_f = Final weight of the concrete cubes in grams

After careful consideration of the effect of coffee grounds in concrete mortar, the SCG0.75 mix was chosen to be cast for the final SCG ventilation product. To measure the indoor temperature, two cubicles were constructed using SCG0.75 and CTRL specimens for the front face of the cubicle. The rest of the faces of the cubicles were constructed using sand brick. The cubicle size is 100 cm x 100 cm x 100 cm. A plywood was used as a roof and placed on top of the cubicle, and a thermocouple sensor was put on top of the roof to measure the outdoor temperature. While indoor and outdoor temperatures were being monitored, a data logger was employed to gather and store data. The temperature sensor, a thermocouple, is made of two different metals joined at one end. A voltage is created when the junction of the two metals is heated or cooled, and it can be related to the temperature. A thermocouple is a versatile, low-cost, easy-to-use temperature sensor used in many different temperature-measuring processes. The monitoring took place over seven days, with data being gathered in real-time every hour. The experimental setup is shown in Fig. (2).

Fig. (2). SCG prototype model for temperature monitoring.

Fig. (3). Flow value on different percentages of SCG.

Fig. (3) shows the flow value on the different percentages of SCG based on the flow table test. Based on the result, the SCG incorporated in the mix has affected the workability of the mortar mix. The CTRL specimen has recorded a flow value of 89%, whereas the increase in the SCG percentage recorded a reduction from SCG0.5 up to SCG0.75 with 64% and 48%, respectively. This indicates the reduction in workability due to the increase in the percentage of SCG. However, there is a steady increase in the percentage from SCG1 until SCG4, with 68% and 129% respectively. Even though the mix became drier, it could disperse uniformly. The vibration from the flow table test allows the mortar to flow better in higher percentages. However, the mix was not in a very liquid state. Too high a percentage of coffee grounds in the mortar will not allow it to set very well due to its poor cohesiveness. According to the research by Lee et al. [18], they have observed a reduced workability in their SCG mortar mixture as the SCG incorporated was increased. At the water-cement ratio of 0.44, a significant reduction of workability was observed when their sample of 6% SCG by weight of cement was mixed. Similar results were observed with the 2% SCG sample in this experiment, which can be attributed to the high hygroscopic property of the SCGs.

Fig. (4) shows the compressive strength test result on mortar with different percentages of SCG. After 7, 28, and 45 days of water curing, the specimens were tested. Based on the result, the SCG incorporated in the mix has shown a significant effect on the strength performance of the mortar. The increase in the percentage of SCG has shown a significant decrease in strength performance. Based on the 7-day result shown in Fig. (4), the CTRL specimen has recorded the highest value of 30.71 MPa. On the other hand, all the SCG specimens recorded a lesser strength value than CTRL, with SCG4 recording the lowest strength with only 0.28 MPa. The overall result on 28 days has shown some strength increment in all specimens compared to the 7-day result. However, a similar trend was shown in all SCG specimens, where a significant reduction in strength was recorded with the increase in SCG percentage. The CTRL specimen has shown the highest value at both 28 days of water curing at 42.381 MPa, whereas the SCG4 recorded the lowest value with the strength of 0.57 MPa. This reduction in strength could be attributed to the dry mix produced when more SCG content was added. The physical properties of untreated SCGs are water-reacted. Thus, their total pore volume and specific surface are lower than fresh coffee, making them non-porous materials, as reviewed by Siberian et al. [30]. However, the SCG used in this study has been treated by oven drying at 100 ^oC. Therefore, the porosity of the SCG has been increased, which affects the ability to trap water and thus prevent the mortar from drying out.

Furthermore, when more SCG was added to the mix, it became dry because the water was trapped in SCG particles. This finding was also reported by Lee et al. [17], which found that adding more SCG to the mortar will significantly decrease the strength. This phenomenon can be attributed to the hydration reaction not being completely fulfilled due to the porous behavior. Incorporating SCG in mortar greatly influences the water-cement ratio and decreases it as the coffee grounds absorb the water in the mix. The optimum water-cement ratio is between 0.45 and 0.6, and the greater the addition of coffee grounds, the lower the compressive strength. This finding was also reported by Roychand et al. [11], who discovered that the samples with higher incorporation of SCG by weight of cement produced a lower compressive strength than the control specimen. On the other hand, the results from this study have shown that all the SCG specimens recorded a comparable compressive strength after 45 days of water curing compared to 28 days of water curing. It is inferred that there is no substantial compressive strength improvement of the mortar in a longer water curing duration. There's even a slight strength reduction due to the extended duration of water curing.

Fig. (4). Compressive strength test on different SCG percentage.

Fig. (5). Water absorption percentage on different SCG percentage.

Fig. (5) shows the water absorption percentage on different SCG percentages. The reading was taken after 30 minutes and 24 hours of testing. Based on the result, there was a steady decrease in water absorption percentage when more percentage of SCG was added to the mix after 30 minutes of the test. A similar trend was recorded on 24-hour data where there was a clear trend of a decrease in water absorption percentage when more SCG were added to the mix. Interestingly, the water absorption decreases linearly when more SCG is added to the mix. This is probably due to the water absorbed and retained during curing. According to Arulrajah et al. [31], due to their organic composition and porous structure, SCGs have been observed to have a high water retention capacity. Technically, the SCG's water absorption varies based on a few parameters, including particle size, moisture content, and processing techniques. Kua et al. [32] observed a decrease in the water absorption rate when adding more percentage of SCG to the mix. Furthermore, in the specimen with higher incorporations of SCGs, the reduction in water absorption rate can be attributed to denser microstructures in the material, which prevent water from easily penetrating the mortar. However, after a certain percentage of high SCG incorporation, the trend of water absorption might increase. This is probably due to poor cohesiveness and workability, which resulted in poor hydration, leading to the sample having larger pores for water to penetrate.

Fig. (6). Relationship between compressive strength and dry density of SCG cement mortar.

Fig. (7). The final product of the SCG ventilation block.

Further analysis was carried out to identify the correlation between dry density and the compressive strength of SCG mortar and compare it to the CTRL specimen. The value of the dry density of all specimens is tabulated in Table 4. The dry density of the mortar is observed to be reduced by adding coffee grounds to the mortar mix. This is probably due to the SCG having a lower specific gravity than cement and sand; adding more to the mixture also lowers its dry density. SCG decreases the mortar's density and strength since it also increases its air content and porosity. A similar result was obtained by Charai et al. [33]; the dry density of its mortar reduces when more SCG is added to the mix design. There might be potential benefits for the production of ventilation blocks as they may have a reduced weight as a final product and reduce their loads on the brick wall and structural members. The dry density and strength of the SCG cement mortar are positively correlated, as shown in Fig. (6). A higher dry density generally results in stronger materials. In contrast, a lower dry density causes weaker materials and more porosity. The amount of air voids to the overall volume of the mortar is known as porosity. A mortar with a higher porosity may be less durable since it will be more vulnerable to chemical and water damage.

After carefully considering the effect of coffee grounds in concrete mortar, the SCG0.75 mix design of mortar was chosen. This selection is based on workability, strength, and water absorption performance. The flow table test showed a 48% flow ability. Even though it was not ideal, it was still workable enough and produced a nice, smooth finish for the concrete blocks cast, which is suitable for the ventilation block as a marketable product. In addition, the compressive strength was recorded at an average of 10.714 MPa, 12.547 MPa, and 14.809 MPa at 7, 28 and 45 days of water curing, respectively. These results have indicated that the SCG0.75 has passed the minimum requirement for blocks as it is above the average compressive strength of blocks at 8 MPa. Furthermore, the water absorption percentage is 3.575% after 30 minutes and 6.107% after 24 hours of immersion in a water bath. These results are suitable, considering that the blocks' average water absorption percentage should be less than 20%. The blocks can absorb moisture from the surroundings if the water absorption rate is too high, resulting in structural damage and a shorter lifespan. The final product of the SCG ventilation block is shown in Fig. (7).

Fig. (8) shows the indoor temperature performance of the SCG and CTRL ventilation block cubicles. The temperature monitoring started at midnight on 8th May 2023 and lasted 168 hours. The data was recorded at every hour and stored in the data logger. Based on the figure, the indoor temperature of both cubicles exhibits a similar trend, which generally follows the outdoor temperature. However, the CTRL indoor temperature was generally higher than the SCG cubicle during the mid-day by about 1 ^oC. The indoor temperature range for the SCG ventilation block is from 34 ^oC to 22 ^oC, whereas the CTRL ventilation block ranges from 35 ^oC to 23 ^oC. For reference, the outdoor temperature generally ranges from 33 ^oC to 26 ^oC. These results show a little reduction in indoor temperature for the SCG ventilation block compared to the CTRL ventilation block, which indicates that the SCG ventilation block has good thermal insulation. The temperature reduction is probably due to the reduction in the thermal conductivity of the ventilation block as a result of adding the SCG into the mix. Lower thermal conductivity indicates that the block can reduce the amount of heat transferred through it; in other words, they are good insulators. This finding is in line with Lachheb et al. [14], who investigated how SCGs affected the thermal characteristics of plaster composites and discovered that thermal conductivity significantly decreased when SCG content was increased. In particular, the thermal conductivity decreased from 0.5 to 0.31 W/m.K by increasing the SCG content in the plaster composites from 0 to 6%. Another study by Velasco et al. [13] discovered that by adding 17% of SCG-fired clay brick, the thermal conductivity can be reduced by up to 50%. However, adding too much of the SCG will reduce the strength of the block. This is because porosity affects compressive strength and the proportion of water absorption, which are other factors that affect the usability of the bricks.

A statistical analysis was performed to determine if there is a significant difference in temperature reduction between SCG Blocks and CTRL Blocks. A paired samples t-test was performed using statistical software (SPSS) to test this hypothesis. Based on the analysis, there was a significant difference in temperature reduction between SCG Blocks (M = 26.0, SD = 2.72) and CTRL Blocks (M = 27.7, SD = 3.09); t (167) = -22.97, p = .000. The details of the t-test computation are shown in Table 5.

Fig. (8). Temperature monitoring of the SCG and CTRL ventilation block.