WASTE GENERATED DURING SANDCRETE BLOCK PRODUCTION

INTRODUCTION – SANDCRETE BLOCK

Sandccrete blocks are made from a mixture of river sand, cement and water. They are used throughout Nigeria and in most African countries. Sandcrete blocks are widely used in Nigeria as walling units. However various waste are generated during the cause of producing sandcrete block which makes the quality of blocks produced to differs from each manufacturer due to the different methods employed in the production. This research focuses on the impact of lean construction on the various waste generated during sandcrete block production.

WASTE GENERATED DURING SANDCRETE BLOCK PRODUCTION

Construction waste has been defined by different studies in different ways. According to production philosophy, waste is described as any inefficiency that results from the use of equipment, materials, labour, or capital in larger quantities than those considered as necessary in the production of a building. Waste consists of both the incidence of material losses and unnecessary work execution, which lead to additional costs but do not add value to the product (Polat and Ballard, 2004).

Waste can also be defined as any losses produced by activities that generate or lead to direct or indirect costs, but do not add value to the product from the point of view of the client (Alwi et al., 2002; Formoso et al., 1999).

According to Polat and Ballard (2004), waste could be simply defined as that which can be eliminated without reducing customer value. It can be activities, rules, resources, etc. According to Macomber and Howell (2004), waste is said be anything that did not add value. More precisely, waste is the use of effort or the using-up of resources without producing value. After categorizing waste to seven types by Ohno (1994), Womack and Jones (1996) defined waste as any activity that consume sources and does not produce any additional value.

Construction waste can be classified into three main types; material waste, time waste and w labour waste (Al-Moghany, 2006; Ekanayake and Ofori, 2000). However, Sandcrete block production is also characterized by construction wastes which are classified according to the three wastes below:

1. Material Waste

Material wastes in construction industry refer to materials from construction sites that are not desirable or unuseful for the purpose of construction and have to be discarded for whatever reason (Yahya and Boussabaine, 2006). According to Ofori and Ekanayake (2000), material waste in construction site is defined as any material apart from earth materials, that needs to be transported somewhere else from the construction site or used on the site itself for another purpose other than the intended purpose of the project as a result of damage, excess or as a result of non-compliance with the specifications, or which is a by-product of the construction process.

2 .Time Waste

Time waste (waiting) is any idle time for workers or machines due to inefficient or bottlenecks production flow on the construction site. Waiting time also includes small delays between processing of units. Time waste generate a significant cost insofar as it increases labor costs and depreciation costs per unit of output are in general known as: waiting for decision, waiting for parts or direction, waiting for information or data, waiting for supplies and waiting for recommendations.

Time waste (waiting) in sandcrete block production is due to:
1. Rework that don’t comply with production specifications.
2. Rework due to workers’ mistakes.
3. Delays in passing of information to the production crew on products.
4. Waiting for workers or materials or equipments to arrive.
5. Equipment frequently breakdown.
7. Delay in commencement of production.
8. Delay in performing testing and inspection by the production manager.
9. Work suspension by the owner.
10. Change orders.

3. Labour Waste

Labour waste can be described as any unnecessary walking or physical motions by workers which divert them from actual processing work. For example, this might include walking around the construction site to look for a tool, or even unnecessary or difficult physical movements, due to poorly designed ergonomics, which slow down the workers. Unnecessary movement (walking, lifting, reaching, etc.) wastes energy and time such as going to warehouse to get parts or walking back and forth between equipment and a truck to get tools or parts.

Labour wastes in sandcrete block production are characterized by:
1. Poor procurement schedule of materials.
2. Unnecessary material handling.
3. Ineffectiveness of tradesmen.
4. Long distance between place of production and place of storage.
5. Poor material distribution on site.
6. Lack of properly maintained pathways.
7. Motion difficulties by workers on construction site.