Life-cycle assessment of compressed bricks using Cameron Highlands reservoir sediment as primary material

Disposal of dredged sediments has recently been linked to environmental and health issues, rather than bringing any economic value to the country. Furthermore, the overexploitation of clay for brick production is destructive to the environment. Hence, it is essential to develop a decisive method to minimize the land and water pollution resulting from improper disposal as well as lessening the consumption of natural resources in the brick production. The key objective of this study is to identify environmental impacts of compressed bricks using Cameron Highlands reservoir sediment to replace clay in the compressed brick. The life cycle assessment is conducted in a cradle-to-gate manner. This study also presents the avoided process of recycled sediments in the life cycle assessment. The damage categories are quantified in terms of human health, ecosystem and resource availability by using ReCiPe Endpoint indicators. According to the results of the life cycle assessment, the compressed sediment brick is favourable from an environmental perspective. In comparison to compressed clay brick, the compressed sediment brick offers promising options for the long-term because it contributes high environmental performance among all the impact and damage categories assessed in this study.


Introduction
Brick plays a pivotal role in the building and construction sector. Studies have proven that the consumption rate of raw materials for construction industry is approximately 3000 Mt/year which is equivalent to 50% by weight of the global raw material resource [1]. The production of conventional bricks is estimated at 1500 billion units annually for construction purposes [2]. The fired clay brick contributes significant greenhouse gas (GHG) emission which directly causes acid rains, global warming and climate change [3]. Thus, the environmental issues evolved from the manufacturing process of brick have become the main focus due to the rise of environmental concern. The proper selection of brick material is crucial for sustainable development in the brick industry.
In recent years, several studies have discussed the topic regarding the adoption of Cameron Highland reservoir sediments to replace compressed clay bricks [4,5]. This is due to the fact that the sediment trapped in the reservoir drastically reduces the life expectancy of the reservoir. For instance, the storage capacity of Jor reservoir, Cameron Highlands experienced a reduction of 53% in 2018 in comparison to the original design capacity of 3.85 million m 3 [6]. Hence, dredging of the sediments is one of the sedimentation control alternatives to restore the original intended storage capacity of Cameron Highland reservoir [7]. However, the disposal of dredged sediment to landfill brings adverse effects to the environment. When the dredged sediments are deposited in the disposal site, the leaching of contaminants affects the surrounding aquatic life and agricultural activities. Thus, the studies have been carried out to exploit the reservoir sediment in construction materials.
The study on properties of Cameron Highland reservoir sediment has been performed to investigate the potential usage of compressed sediment brick [8]. The sources of sediment are extracted from the Cameron Highlands reservoir. The properties of compressed sediment brick are tested based on the allocated mix proportions of sediment silt, sediment sand and cement. Based on the result obtained, the most desired mix proportion of reservoir sediment is constituted of 70% sediment silt, 20% sediment sand and 10% cement [8]. It contains a relatively low concentration of heavy metals that show the absence of arsenic, chromium and zinc in the Toxicity Characteristic Leaching Procedure (TCLP). Hence, it completely adheres to United States Environmental Protection Agency (US EPA) regulatory limits which indicates the unavailability of hazardous content in the sediments. Thus, the compressed sediment brick is safe to be applied to the construction materials.
However, there are fewer researchers applying life cycle assessment (LCA) in their investigation as there is a limitation of database and information for the construction materials such as compressed sediment brick [9]. As mentioned in GlobalABC Regional Roadmap for Buildings and Construction in Asia, the ambitious regulations on LCA must be strictly executed for all building and construction sectors in 2030 [10]. This is because the existing project seldom takes LCA into consideration during the construction phase.
. Some studies have adopted LCA on the comparison between fired clay brick and harbour dredged sediment brick. To date, there are no reliable studies to signify and compare the life cycle impacts of compressed clay brick and compressed sediment brick. Therefore, the LCA method will be fully utilised to present the first reliable result for the ecological impact of compressed sediment bricks. The attempt of this study is to examine the compressed bricks made of Cameron Highland reservoir sediments and their corresponding effects on the environment.

Goal and scope definition of LCA
According to ISO 14040, the definition of goal and scope is typically used to determine the intention of LCA and the probable outcomes of the research [11]. The main purpose of this life cycle assessment study is to determine the environmental impacts from the productions of compressed clay brick and compressed sediment brick. For this study, 1kg of brick has been applied as a functional unit that serves as the base for environmental assessment of compressed clay brick and compressed sediment brick.
The system boundaries of the entire production procedures should be satisfactorily defined to make sure that the scope, extent and depth of the study are coherent and appropriate to undertake the specified goal. In this study, the system boundary is constrained to a cradle-to-gate assessment that only involves partial life cycle of a product from the extraction of raw material, transportation of raw materials to production plant until the manufacturing of products. However, the product usage and disposal of the product are not included in this study. Figure 1 signifies the expanded boundary and system boundary of the compressed clay brick and compressed sediment brick. The whole life cycle assessment of the compressed clay brick is indicated by using the blue rectangular box. In contrast, the red rectangular box represents all the stages of compressed sediment brick's life. The black solid box refers to the whole system boundary of compressed clay brick and compressed sediment brick where processes from the extraction of raw materials until the manufacturing of brick products are taken into consideration. Furthermore, the black dotted line is used to highlight the expanded boundary.

Life cycle inventory
The second stage of the LCA is the life cycle inventory which is concerned with gathering the relevant information in order to accomplish the goals of the study. In this study, the data for the mix proportion of compressed clay brick (C70 and C90) and compressed sediment brick (Mix4) are retrieved from the study by Ean et.al. [8,12,13]. The mix proportion for the compressed clay brick and compressed sediment brick used in this study is shown in Table 1.
Most of the data are obtained from the Ecoinvent version 3.5 database. The model system that has been selected in this study is the Allocation at the Point of Substitution (APOS) model. Table 2 shows the origin of the dataset in Ecoinvent. As the database for compressed sediment brick production is unavailable in Ecoinvent version 3.5, some of the inputs and outputs will be retrieved from the study on compressed sediment brick production completed by Ean [13]. The assumption on the transportation distance of raw materials to the brick production plant is almost 13.6 km. Furthermore, the assumption for the total distance of transporting dredged sediment silt and sand from Sultan Abu Bakar Dam to landfill are roughly 1.49 km and 2.34 km respectively. Prior to the brick production plant, the dredged samples are removed from the sediment disposal regions that have been excavated, deposited and settled for a minimum period of three months. The transportation distance of dredged sediments from the disposal site to the brick production plant is measured based on Google Earth. It is assumed that the transportation distance of dredged sediment silt from the disposal site to the brick production plant is approximately 1 km, while the transportation distance of dredged sediment sand from the disposal site to the brick factory is 2.42 km.
In the system boundary, it is found that the normal sand will be sieved first before proceeding to the production of compressed clay brick. The assumption for the total energy consumption of sieving normal sand and drying of clay is 0.03380 kWh [14]. In addition, the input data for the whole manufacturing process flow of one kilogram of dredged sediment brick involves drying of sediment, sieving sediment sand, grounding sediment silt, mixing of sediment brick, compacting sediment brick and production of sediment bricks. Thus, the electricity consumption for the entire process is approximately 0.02086 kWh [13]. All the input data for compressed clay brick (C70) will be inserted into openLCA software as shown in Figure 1. Figure 2 represents the input data for compressed clay brick (C90), whereby Figure 3 shows the input data for compressed sediment brick (Mix4) which utilized Cameron Highlands reservoir sediment and will be referred as "compressed sediment brick".

System expansion
System expansion serves as the avoided process method in the life cycle assessment. In other words, it acts as a replacement for allocation [15]. The system boundary is defined in this study by taking into account allocation and system expansion. The processes with a negative sign are often applied to indicate that the environmental burdens resulting from the system expansion are avoided in the production process [16].
In this study, the transportation from the extraction point to landfill and the landfill of dredged sediment are all listed as an avoided process approach in the production of sediment brick. Therefore, there is a decrease in landfill waste as a result of avoiding the disposal of sediment in the landfill. Apart from that, the transportation distance of recycled sediment sand and sediment silt from the dam to landfill stated in respective Figure 4 and Figure 5 is recorded as a negative value. Thus, the cost savings of transportation are expressed by the negative value for transportation. This is due to the fact that the reduction in expenses of dumping sediment silt and sediment sand in landfill as they are no longer needed to be sent to landfill.

Life cycle impact assessment
Life Cycle Impact Assessment (LCIA) is one of the stages in the life cycle assessment. The key goal of LCIA is to assess the possible impacts after converting the results of the LCI into a quantitative description of the environment. ReCiPe method is designated as the impact assessment method to be adopted in the present study. ReCiPe model is the most commonly used LCIA method as it is a holistic method to assess the environmental impacts based on both midpoint and endpoint levels [17].
For the evaluation of environmental performance of different bricks production, the impact categories for endpoint have been utilized as environmental indicators for this study. In this study, the impact categories for ReCiPe endpoint indicators include the damage to human health, ecosystems and resource availability.

LCIA under ReCiPe endpoint indicators
The life cycle impact assessment method identifies the processes that have the highest direct contribution to the environment. ReCiPe 2016 Endpoint (H) is selected as an impact assessment method in openLCA software. The optimum sustainable brick can be The damage to human health is defined as the probable effect of environmental degradation on human health. Therefore, it is mainly used to evaluate the incidence rates and number of years of life lost as a result of fatalities. Table 3 graphically represents the environmental impact for various types of brick production with ReCiPe Endpoint method. In the case of damage to human health, both C70 and C90 contribute the same amount of environmental burden of 1.17E-06 DALY. Conversely, Mix4 has the lowest damage value of 9.48E-07 DALY in terms of human health. The damage to ecosystems represents the effects of air emissions, water emissions and emissions to land on the environment and biodiversity over a region annually. It is measured in terms of the quantity of species that have been reduced or diminished over the years. As shown in Table 4, the damage of 1 kg of Mix4 is 5.44E-09 species.yr which is lower than the C70 and C90 with a damage value of6.55E-09 and 6.54E-09 species.yr. respectively.
Resource availability is one of the ReCiPe Endpoint methods that primarily depicts the exhaustion of the natural resources such as raw materials and energy supplies which poses a serious toll on the wellbeing of the population. In this study, the resource availability is derived from the fossil resource scarcity and mineral resource scarcity. As shown in Table  5, the environmental impacts from the Mix4 are lower than C70 and C90 resulting from ReCiPe Endpoint methods. C70 reveals almost double impact in comparison to Mix4.  It is noticeable that Mix4 reflects positive impacts (negative value) in all the endpoint damage categories. This is because the recycled sediment sand and recycled sediment silt are adopted to replace clay used in the brick production. The sediments present a negative damage value which indicate the avoided landfill of sediment. Besides, distinct difference of environmental impact between compressed sediment brick and compressed clay brick is found in the category of resource availability, the main contribution comes from the replacement of clay in the brick production. This may be attributed to the overwhelming demands of brick which require a large proportion of clay to produce conventional brick. To satisfy the demand-supply gap, the over-exploitation of clay causes damage to land resources [18]. Besides, the source of clay will be exhausted soon due to the use of topsoil [19]. In short, Mix4 is a sustainable brick as sediments act as the clay replacement in the brick production which reduces the scarcity of raw materials.

Environmental impacts and engineering properties
In this study, the relative indicator results are utilized as a mean to select the optimum brick with the least environmental burden. The upper limit score for each indicator is fixed to 100%, and the outcomes of other alternatives are presented with regards to this score. Figure 6 displays the relative indicator results of the respective LCIA categories using ReCiPe Endpoint method. Mix4 shows the lowest environmental impact in all 3 endpoint categories as compared to C70 and C90. Thus, compressed sediment brick produces less environmental impact in comparison with the compressed clay brick. Prior to the broad application of brick, the engineering properties of brick must be tested to ensure that the brick is designed based on the standard specifications. In this study, it is required to evaluate the compressive strength of various types of brick in accordance with ASTM C129 and MS Standard 76. In addition, this study considers the effects of clay replacement by sediments on the compressed brick, namely water absorption and TCLP leachate.
Compressive strength is defined as the ability of brick to endure loads imposed on it without deflection or cracking. Referring to the result of Ean [13], the compressive strength of C70 and C90 is 8.5 MPa and 6.9 MPa respectively. In contrast, Mix4 gains the lowest compressive strength of 6.3 MPa for a curing duration of 28 days but still passes the minimum requirement of 4.12 MPa and 5.2 MPa in ASTM C129 and MS 76 as shown in Figure 7. Thus, it will not affect the overall performance of brick in terms of compressive strength.
The water absorption of Mix4 will be tested in order to measure the amount of water that infiltrates into the brick when it is submerged in water. The water absorption of Mix4 is 15.1 % which complies to ASTM requirements. When the amount of sediment increases, the water absorption increases. As a result, the compressive strength of sediment brick will be reduced. However, Mix4 is still able to reach the minimum ASTM requirements.
Apart from that, it is found that the presence of heavy metal in the sediments is relatively low in concentration. The heavy metal leachability of sediment brick is tested by TCLP in accordance with SW 846. Nonetheless, the result reveals that the concentration of As, Cr, Cu and Zn are within US EPA regulatory limits [8]. Therefore, it is proven as the use of reservoir sediments is the most suitable clay replacement in brick production.

Conclusions
This study stresses on the life cycle assessment of compressed bricks using Cameron Highlands reservoir sediment as a replacement material of clay in compressed brick production. ReCiPe method has been adopted to analyse the effects of compressed sediment / clay brick on the environment in a cradle-to-gate manner. Based on the comparison, it can be concluded that compressed brick that utilized sediments collected from Cameron Highland reservoir (Mix4) is preferable than compressed brick produced by clay. The sediment brick is a more environmentally friendly brick due to low adverse impacts on the environment. Despite the fact that the use of recycled sediments reduces the brick engineering performance marginally, the compressive strength of sediment brick is still complied with the minimum standard requirements. The brick industry is strongly urged to employ reservoir sediments as the clay replacement in compressed brick in order to promote higher green rating of construction material.