Utilization of Sawdust in Concrete Masonry Blocks : A Review

SDC (Sawdust Concrete) was developed in 19century. It has been well recognized due to its lightweight and cost-effectiveness. Presently, developed countries have created opportunities to use wood waste in the concrete construction to reduce the environmental burden. Although SDC has received little consideration as a lightweight masonry block in building works but it has been intensively investigated in many countries for decades. The aim of this review is to summarize the last five years (2012-2016) research work related to utilization of sawdust in concrete masonry. However, it is important to explore existing ideas and approaches developed by previous researchers as a reference and guidance for the future research. There are lots of opportunities to develop lightweight concrete especially throughutilizing sawdust as a fine aggregate replacement material in concrete. However, this review paper is focusing on utilization of sawdust, as  to reduce environmental impacts poses by the waste products of furniture industry and a by-product of wood industry. As a conclusion, this review paper summaries the existing important ideas and useful information for the fellow researchers, as to enhance the utilization of sawdust to produce lightweight masonry units. It is recommended that considerable research is required on the sawdust cement blocks, which can deliver more confidence on their utilization as a green building construction material.

D ue to rapid growth of industrialization, the industrial waste creates the environmental and economic problem associated to their disposal. During the recent years there has been increasing focus on the application of discarded items and by-products from numerous sources in building works. Along with the environment protection, numerous studies were conducted on recycling of waste products as construction resources. Utilization of such waste materials into the building works could be a feasible answer not only to the pollution problem, but also to the INTRODUCTION challenge to high cost of construction materials which are being faced by many developing countries. One of such important waste is the sawdust which is comparatively plentiful and economical.
Sawdust is waste produced by timber industries, obtained from cutting, sawing or grinding of timber in the form of particle Fig. 1. Sawdust incorporated in cement has been familiar as 'sawdust cement' [1]. However, the development of sawdust concrete is still under investigation.
Some of researchers have focused utilization of sawdust with additive materials, chemicals, waste materials, light weight aggregate, sand replacement. However, this paper highlights the possible use of sawdust in masonry concrete blocks as a sand replacement adopted by former researchers from Nigeria, Ghana, Brazil, China, Iraq, Turkey, UK, India, Philippines, France and Malaysia. It is expected that this information can be useful for the new researchers to discover more on sawdust concrete.

PRETREATMENT OF SAWDUST
Although sawdust consists largely of cellulose, comprises soluble sugar, acids, resins, oils and waxes,and extra organic materials. These extractable substances affect the setting of cement, particularly in lean mixes. So, irregular deviations of properties in various kinds of sawdust, the only safe process is to conduct trial tests of available sawdust to observe whether it has desired strength can be produced. Pre-treatment of sawdust is, therefore, essential to ensure that extractable materials in the sawdust do not affect hardening process of the cement. Lime need to be added as 1/6-1/3 volume per volume of cement to the sawdust earlier to mixing [2,7].

REVIEW OF PREVIOUS RESEARCH
The summary of literature reviews of published articles since 2012-2016 has been presented in Tables 1-5. Tables  1-5 are showing previous research work carried out on  SDC to develop the lightweight, cost effective, durable and environmental friendly material for the construction industry. It was observed that the utilization of SDC has a wide capability, use as a sand replacement in concrete which reduces the environmental pollution and creates solution to the sustainable construction material to build cost effective structures.

DISCUSSION ON PREVIOUS FINDINGS
Sawdust pre-treatment is, therefore, necessary to ensure that extractable materials in the sawdust do not affect the hardening process of the cement. Two methods of pretreatment has been discussed by Saeed [7]: boiling sawdust in lime added water and addition of waterproofing material diluted in kerosene to sawdust, the better results were found with second method. According to Paramasivam and Loke [2] the optimum socking time for 'Kempus' sawdust was found to be 60 minute earlier to mixing. However, lime is added 1/6-1/3 volume per volume of cement to the sawdust [2].
Physical properties are the basic characteristics of wood and it is behavior to external influences other than applied forces. This includes grain and texture, density, moisture content, dimensional stability, thermal behavior etc. Awareness of physical properties is thus important, because they can significantly influence the performance and strength of the material used in the structural applications: higher the amount of sawdust lower is the workability [3,5,13,17]. Solid Blocks (100x100x100 mm)

Utilization of Sawdust in Concrete Masonry Blocks: A Review
The optimum replacement of sand with sawdust was found to be 5 %. There is a great tendency towards decreases the thermal conductivity and increases the heat preservation and insulation property in sawdust concrete.
Saeed [7] Iraq 0, 5, 10, 15, 20, 25, 30 and 35% by weight of cement in 1:1 mix. Used water curing for 28days Solid cubes (100x100x100 mm) and Prisms (100x100x500mm) Bond between pretreated sawdust and cement paste is increased due to washing out harmful extractives in sawdust which inhabits setting and hardening of surrounding cement paste. Thus properties of SDC were highly being improved using pretreated sawdust. The compressive and Flexural strength were found increasing up to 50% for sawdust. Water absorption and thermal conductivity were highly be reduced.  With gunny bag curing method for 1:6 ratio by 15% sawdust replacement gives strength of 4.5 N/mm2, density is 2000 kg/m3, which is reasonable and economical to be used for the partition walls in frame structure. Two methods (sprinkler and gunny bag covered) of curing were adopted to evaluate the effect of curing and the result of gunny bag covered method was observed the best results.
Kumar et. al. [11] India  The density of sawdust largely depends on the species of wood. Due to hydrophilic nature, the density of sawdust generally varies from 650-1650 kg/m 3 . The density of sawdust concrete also varies depending upon the type and amount of sawdust used in mix. Using 'Kempas' wood, the dry density of sawdust concrete has been found to be 1490, 930 and 850 kg/m 3 for the mixes with cement to sand ratios of 1:1, 1:2 and 1:3 respectively [2]. However, the density of concrete containing sawdust from rubber tree exhibited 1450, 1280 and 1065 kg/m 3 respectively for the same mix proportions [17]. It can be seen that for higher amount of sawdust, the water absorption increased significantly [10,20].
It is in general agreement that higher the amount, lower the strength development. Like mechanical properties, the compressive strength of concrete is greatly influenced by the type of sawdust in the mix. This has been reflected in the research findings of Paramasivam and Loke, [2] and Awal et. al. [17]. Paramasivam and Loke investigated the concrete containing 'Kempus' tree, where 28 day Slump were observed 40mm, 15mm and 5mm for mix proportions of 1:1,1:2 and 1:3 respectively and density of SDC at 28days were found, for the mix of 1:1, 1:2 and 1:3 are 1450, 1280 and 1065 kg/m3 respectively. Compressive strength at 28 day were observed as 18.65, 17.20 and 12.80 N/mm 2 for 1:1, 1:2 and 1:3 respectively. The tensile strength at 28 day were observed as 2.05, 1.95 and 1.30 N/mm 2 for 1:1, 1:2 and 1:3 respectively. The flexural strength at the age of 28 day were observed as 2.75, 2.20 and 1.90 N/mm 2 for 1:1, 1:2 and 1:3 respectively. The elastic modulus of 17100, 16400 and 11950 N/mm 2 were obtained for the mixes of 1:1, 1:2 and 1:3 respectively.  Because of the very organic nature, concrete made with sawdust needs some modifications. It has been shown [10] that air curing at laboratory conditions produced better results as compared to the curing in immersed conditions. Similar behavior was observed in tension, flexure and modulus of elasticity of sawdust concrete [4,10,[17][18].
The tensile strength of SDC, were investigated though split cylinder test according to ASTM C496/C496M at 7, 14 and 28 day, and the findings were presented in Fig. 3.
It was observed as like the compressive strength, tensile strength also reduced with the growth in the quantity of sawdust [17].
The connection between the compressive and tensile strength has been shown in Fig. 4. It was observed that compressive is relational to the tensile strength. Though, the value of the correlation reduces with the increase in sawdust amount.
All these research findings have, however, been limited to short-term study only. Along with strength investigation of masonry units of particular type, it is also important to study the strength behavior of the masonry wall [21].
Apart from the application in masonry units, the application of sawdust in developing lightweight concrete seems to be a distinctive solution not only to the environmental issue but also to the economic and green construction [22]. However, no experimental data are yet available on the structural performance of masonry wall using sawdust brick or blocks. Hence, it can be utilized as lightweight masonry unit in buildings as a partition wall etc.

FUTURE RECOMMENDATION
To evaluate the in-depth strength performances including aspects of durability have been putting forward recommendation for future research in direction to discover well indulgent of sawdust as a green building material.