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1ST International Conference on Infrastructural Development In Africa (ICIDA), KNUST, Kumasi, Ghana, March 2012 MAKING WALL CONSTRUCTION PROCESS LEAN: THE INTERLOCKING BLOCK SYSTEM AS A TOOL E. Zoya Kpamma1, Z. Mohammed Kamil2, K. Adinkrah-Appiah3 ABSTRACT The building construction industry in Ghana, dominated by the use of the conventional sandcrete blocks in wall construction, is faced with the challenge of delivering products of maximum value to clients at an affordable cost and on time. Addressing this challenge will require adopting lean construction principles towards minimising waste and maximising value in the building construction process. Wall construction is one of the major components of the entire building construction process. Ensuring that the wall construction process is made lean will consequently go a long way to reducing waste and enhancing value delivery to clients in the entire building construction process. This paper seeks to explore the interlocking block wall system as a means of making wall construction lean in the building process. A comparative study of constructing a wall using the hydraform interlocking block system and using the conventional sandcrete block system was undertaken. An observation of the processes was made to identify the extent to which each system fell in line with the principles of lean thinking. It was revealed from the study that the use of the interlocking block system does not only lead to eliminating a number of nonvalue adding activities associated with the use of the conventional sandcrete block, but also make the wall construction process faster and cheaper. It was also observed that the absence of mortar jointing in the interlocking system reduces the quantity of materials, like cement and sand, required in the conventional wall construction process. The interlocking block system could therefore be an appropriate tool for implementing lean thinking Ghana. Keywords: Wall construction; lean thinking; interlocking block; waste; workflow 1.0 INTRODUCTION A major problem facing the construction industry in Ghana is the failure of firms to deliver construction products such as buildings on time and at an affordable cost. High cost and time 1 Lecturer, Department of Building Technology, Sunyani Polytechnic, Sunyani, Ghana, evanskpamma@yahoo.co.uk 2 3 B-Tech Candidate, Department of Building Technology, Sunyani Polytechnic, Sunyani, Ghana Lecturer, Department of Building Technology, Sunyani Polytechnic, Sunyani, Ghana Kpamma et al. overruns as well as poor quality of construction products, according to Westring (1997) and World Bank (1996, 2003), are seen to be associated with construction product delivery process in Ghana. For both public and private sector clients in Ghana, it has become the norm for construction work to drag on well beyond stated completion dates, overrun budget and not deliver the quality of work required (Nicco-Annan, 2006). The growing need for speedy delivery of value, associated with less waste, in the construction project delivery process makes it imperative for firms in the construction industry in Ghana to adopt measures towards reducing waste and maximising value for their clients in the construction process. One of the main components of a building construction is the construction of walls. The walls, enveloping and partitioning buildings, while playing the significant role of ensuring the comfort, privacy and security required within the buildings, contribute to the cost of materials and labour of building construction. Ensuring minimisation of waste in wall construction could therefore contribute to a reduction in the waste generated in the entire building construction process thus increasing value to clients. Building construction projects in Ghana, like urban housing and school buildings, are largely dominated by the use of the sandcrete blocks in masonry wall construction. The conventional process of erecting walls using sandcrete blocks with mortar joints is however observed to be associated with some form of waste generation which needs to tracked and eliminated. The waste generated is manifested in the form of waiting, over processing, raw material inventories, work in progress and so on. The principles of lean thinking seek to reduce waste and maximise value in production processes (Kotelnikov, 2007). Reduction of waste generated during wall construction of buildings can thus be achieved through the application of lean thinking principles in wall construction. One of the strategies of implementing lean thinking in construction process is to attempt to make construction more like manufacturing from where the lean philosophy evolved. According to Koskela (1992) this can be achieved by applying proven standard workflows and associated components, skills etc. The paper seeks to explore the possibility of making wall construction of buildings in Ghana lean by adopting a dry walling system, like the interlocking block wall system, as a substitute to the conventional sandcrete block wall system. KNUST, Kumasi Making Wall Construction Lean 2.0 LEAN THINKING IN CONSTRUCTION The concept of lean thinking originated from the manufacturing sector and focuses on producing in a manner that eliminates defects while using less input in the form of labour, machinery, space and time by reducing the number of conversion activities and movement flows in making a product (Harris and McCaffer, 2001). Many ideas from the manufacturing industry such as lean thinking have been rejected by the construction industry on the basis that construction is different. Howell (1999) in explaining the peculiarity of the construction industry from the manufacturing sector states that “manufacturers make parts that go into projects, but the design and construction of unique and complex projects in highly uncertain environments under great time and schedule pressure is fundamentally different from making “tin cans”. According to Koskela (1992), the construction industry as a result of its peculiarities is often seen in a class of its own, different from manufacturing. These peculiarities, Koskela (1992) further explains, are often presented as reasons - or excuses – for failure to implement such well-established and useful concepts as lean production from the manufacturing sector. While difficult to interpret for construction, the lean thinking concept if adopted as a fundamental concept could be visualised through more accurate preplanning, an increased use of standard components, prefabrication, modular systems and rigorous attention to resource procurement (Harris and McCaffer, 2001). Koskela (1992) also suggests actions like standardizing components, utilizing modularization and prefabrication as well as using enduring teams, as measures to reduce the uniqueness of construction and bring it closer to manufacturing. Warszawski (1990) has further indicated that industrialized building systems provide solutions to be considered in implementing lean thinking in construction, and that construction companies had begun to offer concept buildings (office buildings, schools, day nurseries, etc.), which are pre-engineered solutions that can be adapted to different needs. The concept of lean thinking in construction project delivery seeks to maximize value delivered to customers while minimizing waste. In its basic form, the practice of lean thinking is the systematic elimination of waste (i.e. overproduction, waiting, transportation, inventory, motion, over-processing, defective units) and the implementation of the concepts of continuous flow and customer pull (Kotelnikov, 2007). ICIDA ’2012 Kpamma et al. 2.1 Waste in Construction A number of non-value adding activities are associated with design and construction processes resulting in waste generation. Majority of these wasteful activities consume time and effort without value generation to clients. As a result of this situation, managers of construction activities at the start of construction projects have to deal with many factors that may negatively affect construction processes producing different types of waste (Serpell et al., 1995). Waste here refers to both the incidence of material losses and the execution of unnecessary work that generates additional costs but does not add value to the construction product (Koskela, 1992). In the construction and manufacturing industry waste include, among others, delay times, quality costs, lack of safety, rework, unnecessary transportation, long distances, improper choice of management methods or equipment, as well as poor constructability (Alarcon, 1993; Ishiwata ,1997; Koskela, 1992 and Serpell et al., 1995). Formoso et al (1999) went on to propose their main classification of waste in construction as over production, unwarranted substitution, waiting time, transportation, processing, inventories, movement and defective products. Ohno (1988), who articulated the lean production philosophy and implemented it in Toyota’s production system, classified sources of waste as follows: defects in products, over-production of goods not needed, inventories of goods awaiting further processing or consumption, unnecessary processing, unnecessary movement of people, unnecessary transport of goods, waiting by employees for process equipment to finish its work or for an upstream activity to complete. An eighth category of waste was added by Womack and Jones (1996) as design of goods and services that fail to meet user's needs. 2.2 Workflow in Construction Construction projects can be formulated as a series of work processes linked to each other in a dependent network, with some processes running serially and some running concurrently (Palaniappan et al., 2007). Work in construction projects therefore typically flows from one process as a completed step to the next step to augment the process. Ballard and Howell (1994), Howell et al. (1993), Tommelein et al. (1999), Walsh et al. (2007), and Sawhney et al. (2007) have all, in previous studies, indicated the potential damaging nature of inter-linkages between processes. KNUST, Kumasi Making Wall Construction Lean The concept of flow is one of the core elements of lean thinking towards achieving a complete removal of waste (Picchi and Granja, 2004). It describes an ideal situation of a flowing value devoid of interruptions thus leading to waste elimination and ensuring a reduction in the lead time of generating new products or services (Womack and Jones, 1996). The practical implementation of the concept of flow requires establishing production cells involving models like one piece flow, multi-functional operators, as well as controlled and standardised rhythm for significant productivity gains (Rother and Harris, 2002). The view of flow in production, proposed by the Gilbreth and Gilbreth (1922), has in scientific terms, provided the basis for Just in Time (JIT) and lean production. In the concept of flow, production is viewed as a flow whereby in addition to transformation activities, there are non transformation activities like waiting, inspection and movement. Production management therefore involves reducing the share of non-transformation steps of production flow, especially by reducing variability. In this respect the flow model looks beyond transformation activities by taking non-transformation activities into account in order to improve flow efficiency (Gilbreth and Gilbreth, 1922). The concept of lean thinking in construction, apart from focusing on a systematic elimination of waste, also involves the implementation of the concepts of continuous flow and customer pull (Kotelnikov, 2007). Howell (1999) also identifies organising production as a continuous flow as one of the core concepts of lean production. Improving workflow reliability, according to Ballard (1999), is important for productivity of linked production units, and consequently for project cost and duration. Continuous workflow ensures steady production rates that eliminate the chaos of fragmented stop-and-go production processes (Caldeira, 1999). Production in construction basically involves assembly of components and materials, in which case different material flows are connected to the end product. Koskela (2000) suggested three types of flows in construction. The first type is material flow which involves transportation of components to the site for installation. The second type is location flow whereby one particular trade goes through the different parts of the building or construction site to get work done. The third type is assembly flow involving the sequence of works of assembly and installation. ICIDA ’2012 Kpamma et al. 3.0 THE INTERLOCKING BLOCK SYSTEM Interlocking blocks are different from conventional bricks since they do not require mortar to be laid. The blocks are just laid dry and locked into place. As a result of this characteristic, the process of building walls is faster and requires less skilled labour. Laying the first course in the mortar bed requires that care is taken to ensure that blocks are perfectly horizontal and in a straight line or at right angle corners. Once the base is properly laid, the blocks are stacked dry with the help of a wooden rubber hammer to knock the blocks gently in place (Nasly and Yasin, 2009). The hydraform interlocking block masonry is one building system which almost fulfils all such requirements of sustainability masonry as use of locally available resources (materials and labour), cost-effectiveness, eco-friendly, easy to adopt, faster to build and energy efficient. Hydraform dry stacked interlocking block system enables aesthetic affordable buildings as well as speedy construction of high quality walls in stretcher bond (Bansal, 2010). The interlocking stabilised soil block technology is affordable, environmentally sound, user friendly, versatile in use among others (UN-HABITAT 2009). Almost any type of building can be constructed with interlocking blocks. The main design constraints according to Nasly and Yassin (2009) are however that, the plan should be rectangular and all wall dimensions and openings must be multiples of the width of the block used. All other principles of design and construction such as dimensioning of foundations, protection against rain and ground moisture, ceiling and roof construction and the like, are the same as for other standard building types. The concept of inter locking blocks is based on the following principles: i. The blocks are shaped with protruding parts which fit exactly into recess parts in the blocks placed above such that they are automatically aligned horizontally and vertically (Figures 1 and 2). This makes brick laying possible without specialised skills. ii. Since blocks can be laid dry, no mortar is required and considerable amount of cement is saved KNUST, Kumasi Making Wall Construction Lean Figure 1. Interlocking Block (Bansal, 2010) Figure 2. Placing of Interlocking Block (Bansal, 2010) 4.0 RESEARCH METHOD The research involved a comparative study of the processes involved in constructing walls using the conventional sandcrete blocks and those involved in using the hydraform interlocking dry wall system. A critical observation of the various steps involved in using the conventional sandcrete blocks and the interlocking blocks in wall construction was undertaken. This made it possible to make a comparison of the non-value adding steps associated with conventional ICIDA ’2012 Kpamma et al. sandcrete block wall construction to those associated with interlocking block wall construction. The speed of construction of the walls and labour productivity was also observed and compared. 4.1 Data Collection Procedure The data for the research was obtained by observing the construction of two sets of walls using conventional sandcrete blocks and hydraform interlocking blocks. Each set had two walls joined at 90o to each other and measuring 3000mm x 1500mm each, as shown in Figure 3 below. In both cases a window opening (900mm x 600mm) was fixed within each of the walls. Two masons (A and B, both skilled in conventional sandcrete block wall construction and hydraform 1050 900 1500 900 X 3000 X 600 1050 interlocking block wall construction) were engaged in the process. Section X-X 1050 900 3000 1050 Plan Figure 3: Plan and Section of Typical Walls The first part of the experiment involved the two masons together constructing one set of walls from the conventional sandcrete blocks and also together constructing another set of walls from the interlocking blocks. The second part involved a simultaneous process whereby mason A constructed one set of walls from the conventional sandcrete blocks, while mason B constructed the other set of walls from interlocking blocks. The third part of the experiment was a reverse of the second in which case mason A rather constructed the walls with interlocking blocks while mason B constructed the walls with conventional sandcrete bocks. KNUST, Kumasi Making Wall Construction Lean During each part of the experiment observations were made of the comparative speed of construction between the use of interlocking blocks and sandcrete blocks. Various forms and sources of waste arising from the use of the conventional sandcrete blocks were also observed and compared to those arising from the use of the interlocking blocks. One of the key limitations in the data collection procedure was the fact that, unlike the interlocking block system, it was not possible to build a continuous height of wall above 1500mm with the conventional sandcrete block without allowing the wall to dry and harden to prevent a collapse. This situation limited the study to a wall height of 1500mm. 5.0 FINDINGS 5.1 Wall Construction Process Table 1: Steps Involved in Wall Construction Stage Description Activities (Steps) A General (Preliminary) Preparation A1. Setting out Laying First Course B1. Transporting mortar B A2. Preparation of mortar B2. Spreading base mortar B3. Transporting block units B4. Placing block units in first course B5. Plumbing B6. Levelling B7. Filling and dressing vertical mortar joints C Laying Subsequent Courses C1. Transporting mortar C2. Spreading mortar for the course C3. Transporting block units C4. Placing block units in the course C5. Plumbing C6. Levelling C7. Filling and dressing vertical mortar joint Legend ● Applicable step ○ Eliminated / none-value adding steps ICIDA ’2012 Conventional Block Walling Interlocking Block Walling ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ○ ● ● ● ● ● ● ● ○ ○ ● ● ● ○ ○ Kpamma et al. The standard stages and associated activities (steps) involved in the wall construction process in the use of the conventional sandcrete block and those involved in the use of the interlocking block were observed and recorded as shown in Table 1 above. The steps, as observed, were compared to identify which of them was a non-value adding step (or is eliminated in either of the two wall construction systems) and therefore constituted waste as classified by Formoso et al. (1999), Ohno (1988), and Womack and Jones (1996). As shown in Table 1, the use of the interlocking block system led to the elimination of a number of steps. The step that was eliminated in the laying of the first course was filling and dressing vertical mortar joints. The steps that were eliminated in the subsequent courses included filling and dressing vertical mortar joints, transporting mortar, spreading mortar for a course and levelling. These eliminated steps, also known as non-value adding steps, can be categorised into the various classes of waste as shown below in Table 2. Table 2: Waste Categorisation of Eliminated / None-value adding Steps Category of Waste Filling and dressing vertical mortar joints Over production Unnecessary processing Inventories of goods Unnecessary transportation Unnecessary movement Waiting Defective products Unwarranted substitution Failure to meet needs ■ ■ □ □ □ □ − − − Eliminated / None-value adding Step Transporting Spreading mortar mortar for a course − − □ ■ ■ □ − − − ■ ■ □ □ □ □ − − − Levelling □ ■ − − − □ − − − Legend ■ Direct link □ Consequential / Indirect link − Weak link While some of the eliminated steps are direct manifestations of some category of waste, other steps have consequential or indirect link to some category of waste. For instance “filling and dressing vertical mortar joints” directly manifests as “unnecessary processing” but is also indirectly linked to “waiting” due to the fact that labourers had to wait before vertical jointing KNUST, Kumasi Making Wall Construction Lean and dressing is complete for them to either provide more mortar or blocks. “Transporting mortar” is also directly linked to “unnecessary movement” as a form of waste, but indirectly linked to “waiting” due to the fact that masons had wait for mortar to be supplied to them before they start or continuo vertical or horizontal jointing of blocks. 5.2 Speed of Wall Construction One of the important requirements of the concept of lean thinking is timely delivery of value. The speed at which major building components like walls can be constructed is therefore critical towards ensuring timely delivery of building construction products. The time that was spent to undertake various activities in the construction of the two walling systems was observed and discussed below. 5.2.1 Completion of First Course The time that was spent by mason A, mason B and masons A&B in the construction of the first course of the two walling systems is a shown in Figure 4 below. 0:36 Time Spent (hrs) 0:28 0:21 0:14 0:07 0:00 Mason A Mason B Masons A&B Sandcrete Block Wall 0:20 0:21 0:17 Hydraform Interlocking Block Wall 0:29 0:27 0:24 Figure 4: Time Spent to Complete First Course The time that was spent in the construction of the first course of the interlocking block wall across all the various phases of the study was generally more than the time spent in the construction of the first course of the conventional sandcrete block wall. Averagely about 72% of the time that was used to complete the first course of the interlocking wall was required to complete the first course of the conventional sandcrete block wall. The relatively more time ICIDA ’2012 Kpamma et al. spent in the first course of the interlocking block wall results from the fact that more time was spent in plumbing and levelling the first course to achieve a near perfect alignment in order to avoid coordination problems during the dry bonding (locking of blocks) of subsequent courses. 5.2.2 Completion of Second Course The second and first courses in masonry wall construction are critical in ensuring the requirement of avoidance of continuous vertical joints in wall construction. This is because the rest of the wall after the second course is basically an alternating arrangement of the first and Time spent (hrs) second courses to avoid continuous vertical joints. 0:25 0:23 0:20 0:17 0:14 0:11 0:08 0:05 0:02 0:00 Mason A Mason B Masons A&B Sandcrete Block Wall 0:23 0:22 0:13 Hydraform Interlocking Block Wall 0:04 0:05 0:02 Figure 5: Time Spent to Complete Second Course It can be seen from Figure 5 that, unlike the first courses, in the case of the second courses, the time spent for the interlocking block walls was not only less than that for the conventional sandcrete block walls but also reduced drastically. An average of about 18% of the time that was used to complete a second course of the conventional sandcrete block walls was used to complete a second course of the interlocking block walls. The significant drop in the time spent in the second courses of the interlocking block system can be attributed to the elimination of non-value adding steps like horizontal spreading of mortar, vertical mortar jointing, dressing of mortar joints and levelling. KNUST, Kumasi Making Wall Construction Lean 5.2.3 Completion of Subsequent Courses after First Course The total time spent to complete the rest of the courses of the walls after the first course has been laid is shown in Figure 6 below. The time spent for the subsequent course of the interlocking block wall for all various stages of the study was seen to be less than the time spent on the subsequent courses of the conventional sandcrete block. After the first course, almost 32% of the time spent on the subsequent courses of the conventional sandcrete block wall was spent on the Time spent (hrs) subsequent courses of the interlocking block wall. 2:52 2:24 1:55 1:26 0:57 0:28 0:00 Mason A Mason B Masons A&B Sandcrete Block Wall 2:42 2:39 1:33 Hydraform Interlocking Block Wall 0:54 1:00 0:24 Figure 6: Time Spent to Complete Subsequent Courses after First Course 5.2.4 Completion of the Entire Wall The duration for the completion of the entire wall using the conventional sandcrete block and Time spent (hrs) using the interlocking block is illustrated in Figure 7 below. 3:21 2:52 2:24 1:55 1:26 0:57 0:28 0:00 Mason A Mason B Masons A&B Sandcrete Block Wall 3:02 3:00 1:50 Hydraform Interlocking Block Wall 1:23 1:27 0:48 Figure 7: Time Spent to Complete Entire Wall ICIDA ’2012 Kpamma et al. It can be seen clearly that the time that was spent in constructing an entire wall using the interlocking block was far less than the time that was required to complete an entire wall using the conventional sandcrete block. Just about 46% of the time that was spent on building the entire wall using the conventional sandcrete block was required to build the entire wall using the interlocking block. 5.3 Labour Output The output of the masons in constructing the walls using the conventional sandcrete block and the interlocking block is shown in Table 3 below. Table 3: Output of Masons Mason A B Mean A&B Output (m2/hr) Conventional sandcrete block 3.30 3.30 3.30 5.46 Interlocking block 7.20 6.90 7.05 12.50 The labour output figures in Table 3 indicate that the productivity of the masons was higher in the use of the interlocking block in wall construction compared to the use of the conventional sandcrete block. The output of the masons was about 54% more when the interlocking block was used compared to when the conventional sandcrete block was used. The better output associated with the use of the interlocking block can be attributed to the fact that there is a high degree of continuous workflow in the interlocking block walling compared to the conventional sandcrete block walling. This situation is directly linked to the absence of mortar jointing in the interlocking system. 5.4 Quantity of Material (Mortar) Usage Mortar was observed to be an important component in the construction of the walls. The use of mortar was common to the two walling systems even though to varying degrees. It can be seen from Figure 8 that the quantity of mortar used for the interlocking block walling was far less than the quantity used for the conventional sandcrete block walling. In the case of the interlocking block walling, mortar was only required to serve as a bed for the first course. The rest of the KNUST, Kumasi Making Wall Construction Lean courses for the interlocking block walling was constructed through dry bonding and did not Mortar used (m3) require mortar. 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 A B A&B Sandcrete Block Wall 0.58 0.64 0.61 Hydraform Interlocking Block Wall 0.04 0.03 0.04 Figure 8: Quantity of Mortar Usage 5.4 Cost of Wall Construction Table 4: Cost of Wall Construction a. Labour Cost Item Description 1. 2. Building first course Spreading mortar for subsequent courses 3. Placing blocks, levelling and plumbing 4. Filling and dressing vertical mortar joints 5. Total labour cost b. Material Cost Item Description 1. 2. Mortar Total material cost c. Total Cost of Wall Construction ICIDA ’2012 Conventional block Average Approximate Time per labour cost @ mason Gh¢0.93/hr (hr) 0.33 0.31 0.52 0.48 Interlocking block Average Approximate Time per labour cost @ mason Gh¢0.93/hr (hr) 0.47 0.44 0.00 0.00 1.20 1.12 0.95 0.88 0.95 0.88 0.00 0.00 2.79 Conventional block Quantity Approximate (m3) mortar cost @ Gh¢222.47/m3 0.61 135.71 135.71 138.50 1.32 Interlocking block Quantity Approximate (m3) mortar cost @ Gh¢222.47/m3 0.03 6.67 6.67 8.99 Kpamma et al. As shown in Table 4, the cost associated with the process of constructing a wall with the interlocking block is far lower compared to using the conventional sandcrete block. About 6.5% of the cost that was involved in erecting the wall using the conventional sandcrete block was required for building the wall using the interlocking block. Despite the fact that a relatively lower cost of labour played a role, a significant portion of the cost savings in the use of the interlocking block came from the significantly low quantity of mortar required. 6.0 DISCUSSION 6.1 Wall Construction Process One of the key concerns of lean thinking is the minimisation of process waste. The core concept behind lean production, according to Caldeira (1999), is to create a flow among value adding work steps while eliminating non-value adding steps. The study revealed that the use of the conventional sandcrete block, which currently dominates walling materials (especially in urban housing) in Ghana, is associated with a number of non-value adding steps compared to the interlocking blocks. The use of the interlocking block walling system is therefore a positive attempt towards a lean process due to the fact that a number of non-value adding steps, like vertical mortar jointing and dressing, are eliminated. Various forms of waste, manifesting as unnecessary processing, overproduction, waiting, unnecessary movement, inventories and so on, result from the use of the traditional sandcrete block. The use of dry bonding for the interlocking block work leads to a minimisation of these forms of waste. Movement of people and materials related to mortar jointing is, for instance, largely reduced. The use of the interlocking system also minimises unnecessary processing and over production as forms of waste since mortar jointing is eliminated especially after the first course. There is also a reduction in waiting and enhancement of continuous workflow arising from the fact that steps like spreading of mortar, levelling, vertical jointing and dressing of joints are virtually absent in the interlocking walling system. Inventories in the form of materials like sand, cement and water to produce mortar for jointing in the case of the conventional sandcrete block is eliminated in the use of the interlocking block. The elimination of the various non-value adding steps in the traditional sandcrete wall construction process and the consequent reduction in the various forms of waste, through the use KNUST, Kumasi Making Wall Construction Lean of the interlocking block, has the benefit of cutting down material and labour requirements with an attendant reduction in construction cost. Another impact of the elimination of the non-value steps in the wall construction process is that, it ensures fast cycle times thus increasing speed of construction. In line with the description of “lean manufacturing” by Kotelnikov (2007) as a shorthand to commitment to eliminating waste, simplifying procedures and speeding up production, the interlocking block could be seen as a worthy tool towards making wall construction process lean. 6.2 Speed of Wall Construction Speedy delivery of value is very important towards ensuring a lean project delivery of construction products. “Lean” is doing more with less: less time among others (Kotelnikov, 2007). The delivery of construction products on time, apart from contributing to a reduction in cost of construction, also enhances value to clients. The results of the study indicate that the pace of wall construction using the interlocking blocks is far more than using the conventional sandcrete block. The elimination of non-value steps like spreading mortar, levelling, vertical mortar jointing and dressing of joints significantly reduces the cycle time of bonding blocks thus increasing the speed of wall construction. Much time is devoted in the interlocking block system for the construction of the first course to ensure near perfect alignment and proper coordination of block units in subsequent courses. Once the first course is properly laid, the building of the subsequent courses simply involves stacking the blocks to interlock. This eliminates the chaos of disjointed stop-and-go production processes associated with the conventional sandcrete blocks and rather focuses on fast cycle times to ensure reliable and continuous workflow. Generally less than half the time that was used to erect a wall using the conventional sandcrete block was required to erect a similar wall using the interlocking block. 6.3 Labour Output / Productivity According to Womack et el. (1991) “lean production” is “lean” because it uses less of everything including labour. The study showed that greater output of masons was achieved in the use of the interlocking block system compared to the conventional sandcrete block system. The output of masons increased by more than 50% when they used the interlocking blocks instead of the conventional sandcrete blocks. The higher output of the masons resulted from the fact that some ICIDA ’2012 Kpamma et al. steps were eliminated in using the interlocking blocks compared to when laying with the traditional sandcrete blocks. The incidence of “waiting”, resulting from the disjointed stop-andgo production processes associated with the conventional sandcrete blocks, was also largely reduced in the case of the interlocking blocks, therefore enhancing output. The idle time of labour in the use of the interlocking block compared to the conventional sandcrete block was also drastically reduced. Unlike the conventional sandcrete block walling system, the continuous workflow nature of the interlocking block walling system took away the intermittent idle times particularly associated with labourers who were engaged to carry blocks and mortar for jointing. The wall construction steps of spreading mortar, vertical jointing, mortar joint dressing and levelling led to the idle time in the use of the conventional sandcrete blocks. 6.3 Material Usage The description of “lean”, according to Kotelnikov (2007), as doing more with fewer inventories, less space, less money and so on, makes the quantity of material usage in the wall construction process important in observing the principles of lean thinking. Apart from the base mortar that is required to link the first course to the floor, no mortar is required for the subsequent courses of the interlocking walling system. The absence of mortar jointing in the interlocking block walling process leads to a significant reduction in the quantity of mortar used compared to the case of the conventional sandcrete block. The insignificant role of mortar in the interlocking block walling process implies that materials like aggregate and cement are not required in the wall construction process. This ensures that inventory and space associated with the wall construction process are reduced to a significant level. There is also some amount of cost savings arising from the reduced use of materials like cement and aggregate as well as the less space required for inventory. 6.3 Cost of Construction The cost of construction process is mainly influenced by inputs like materials and labour. Any attempt at reducing the cost of these two inputs will go a long way to reduce the overall cost of any construction process. As indicated in the discussions above, the use of the interlocking block leads to a significant reduction in the labour and material requirements of the wall construction KNUST, Kumasi Making Wall Construction Lean process compared to the use of the conventional sandcrete block. This situation leads to a far less cost of construction of wall using the interlocking block relative to using the traditional sandcrete block. Between the two cost parameters of labour and materials, the relatively far less cost of construction of interlocking block walls is driven more by the reduction in the use of materials in the form of mortar. It is the less use mortar for jointing which largely contributes to a reduction in the cost of interlocking block wall construction process by about 93% compared to the conventional sandcrete block. 7.0 CONCLUSION The building construction industry in Ghana, particularly the urban housing sector, is dominated by the use of the conventional sandcrete block for wall construction. Various forms of waste have however been observed to be associated with the process of erecting walls using the conventional sandcrete block. This has lead to the need to explore the possibility of adopting other walling systems towards making the wall construction process lean in order to reduce waste and maximise value. A comparative study was conducted between the use of the conventional sandcrete block and the use of the interlocking block to establish the possibility of bringing wall construction process closer to the principles of lean thinking through the adoption of the interlocking block system. The focus of the study was to particularly identify some non-value adding steps in wall construction process associated with the use of the conventional sandcrete block so that those steps could be eliminated through the use of the interlocking block. The study revealed that a number of non-value adding steps like spreading of base mortar for various courses, vertical mortar jointing and levelling, which are associated with the use of conventional sandcrete block, could be eliminated when the interlocking block is used for wall construction. Such various forms of waste as over-production, unnecessary movement, unnecessary processing, inventories and waiting, seen to be associated with the use of the conventional blocks, are minimised to a large extent when the interlocking block is in use. ICIDA ’2012 Kpamma et al. The elimination of the various non-value adding steps associated with the conventional sandcrete block wall construction through the use of the interlocking block system reduces the cycle time of block bonding thus increasing the speed of wall construction. Besides, the elimination of the non-value adding steps leads to an enhanced labour output, thus making more to be achieved with less labour in wall construction. There is also a significant reduction in the material requirement for the interlocking block wall construction process due to the absence of mortar jointing. Reduction in the labour and material requirements in the interlocking block wall construction process makes the cost associated with the process of building walls using the interlocking blocks far less. The interlocking block is in no doubt a worthy tool towards making wall construction process lean due to the establishment of its elimination of non-value adding steps in wall construction, as well increasing speed of construction while reducing labour and material requirements. One challenge to its adoption in Ghana is however the fact that the interlocking block work technology is not common and skilled labour for its application is not readily available. This may call for the need for more training of artisans in this technology. The curricula of Technical and Vocational Educational Training (TVET) institutions offering training in masonry work needs to be revised to include training models in the interlocking block work. A modular approach to building design, using the interlocking block as the basic module, also needs to be adopted for an effective and efficient use of the interlocking block in building construction. REFERENCES Alarcon, J. V., 1993, Input- Output Analysis with Special Reference to Developing Countries, Institute of Social Studies, The Hague, the Netherlands. Ballard, G. and G. Howell., 1994, Implementing Lean Construction: Stabilizing Work Flow. Second Annual Conference on Lean Construction, Catolica Universi- dad de Chile Santiago, Chile, September 1994. Ballard, G., 1999, Improving Workflow Reliability, IGLC-7 proceedings University of California, Berkeley, CA, USA276. Bansal, D., 2010, Interlocking Dry Stacked Masonry, 8th International Masonry Conference, Dresden. KNUST, Kumasi Making Wall Construction Lean Caldeira, E., 1999, Learn Construction, http://www.housingzone.com/info/CA379761.html, 10/03/07, 8pm GMT Formoso, C.T., Isatto, E.L., and Hirota, E.H., 1999, Method for waste Control in the Building Industry, IGLC-7 proceedings, University of California, Berkeley, CA, USA276. Gilbreth, F.B. and Gilbreth, L.M., 1922, Process charts and their place in management, Mechanical Engineering, January (70) 38-41. Harris F. & McCaffer R., 2001, Modern Construction Management, Blackwell Science Ltd., UK pp. 31-32. Howell, G., A. Laufer. and G. Ballard., 1993, Interaction Between Sub cycles: One Key to Improved Method., Journal of Construction Engineering and Manage- ment, ASCE, 119(4), 714-728. Howell, G., 1999, Managing Construction: The Lean Perspective, The Lean Construction Chronicle, Spring 1999, Lean Construction Institute, Ketchum, pp.1-3. http://www.leanconstruction.org/pdf/1999Chronicle.pdf. Ishiwata, J., 1997, IE for the shop floor: Productivity Through Process Analysis, ThomsonShore, Inc. Koskela, L., 1992, Application of the New Production Philosophy to Construction, Technical Report No. 72, CIFE, Dept. of Civil Engrg., Stanford University, CA, pp.75. http://www.ce.berkeley.edu/~tommelein/Koskela-TR72.pdf. Koskela, L., 2000, An Exploration towards a Production Theory and its Application to Construction, Espoo 2000. Technical Research Centre of Finland, VTT Publications 408. Kotelnikov, V., 2007, Lean Production – Doing More With Less, Ten3 Business eCoach, version 2007a. http://www.1000ventures.com, 10/03/07, 8pm GMT. Nasly M.A., Yassin A.A.M., 2009, Sustainable Housing Using an Innovative Interlocking Block Building System, In: Proceedings of the Fifth National Conference on Civil Engineering (AWAM ’09): Towards Sustainable Development, Kuala Lumpur, Malaysia. Nicco-Annan, J., 2006, Partnering in Construction. The Quantity Surveyor, Issue 1, 2006. pp.14-19. ICIDA ’2012 Kpamma et al. Ohno, T., 1988, Toyota Production System: Beyond Large-Scale Production, Productivity Press, Cambridge, Massachusetts. Palaniappan, S., Sawhney, A., Walsh, K. D. and Bashford, H. H. (2007). Special Purpose Simulation Template for Workflow Analysis in Construction. Proceedings of the 2007 Winter Simulation Conference. Picchi, F.A. and Granja, A.D., 2004, Construction Sites: Using Lean Principles to Seek Broader Implementations. Proceedings of the 12th IGLC conference, Elsinore, Denmark. Rother, M. and Harris, R., 2002, Creating Continuous Flow. Brookline Massachusetts, USA, pp.104. Sawhney, A., K.D. Walsh, H.H. Bashford, and Palaniappan, S., 2007, Impact of Inspected Buffers on Production Parameters of Construction Processes. Journal of Construction Engineering and Management, ASCE . Serpell, A.; Venturi, A. and Contreras, J., 1995, Characterization of Waste in Building Construction Projects”. In Alarcon, Luis (1997, Ed.) Lean Construction, A.A. Balkema, Netherlands. Tommelein, I.D., Riley, D. and Howell, G.A., 1999, Parade Game: Impact of Work Flow Variability on Trade Performance, Journal of Construction Engineering and Management, ASCE, 125(5), 304–310. UN-HABITAT, 2009, Interlocking Stabilised Soil Blocks: Appropriate Earth Technologies in Uganda, United Nations Human Settlement Programme, Nairobi, Kenya. Walsh, K.D., A. Sawhney, and H.H. Bashford., 2007, Pro- duction Equations for UnsteadyState Construction Processes. Journal of Construction Engineering and Management, ASCE, 133(3), 254-261. Warszawski, A., 1990, Industrialization and Robotics in Buiding: A Managerial Approach. Harper & Row, New York. pp.466. Westring, G., 1997, Ghana Public Procurement Reform. An Audit Report prepared for the World Bank, Stockholm: Advokatfirman Cederquist KB. Womack, J.P., Jones, D.T., and Roos, D., 1991, The Machine That Changed The World: The Story of Lean Production. New York. 1st Harper Perennial Ed. Womack, J.P. and Jones, D.T., 1996, Lean Thinking: Banish Waste and Create Wealth in your Corporation. Simon and Schuster, New York, NY. pp.350. KNUST, Kumasi Making Wall Construction Lean World Bank, 1996, Ghana 1996 Country Procurement Assessment Report. Washington, D.C.: The World Bank. World Bank, 2003, Ghana 2003 Country Procurement Assessment Report. Washington, DC: Ghana Country Department, The World Bank. ICIDA ’2012