Title : “The Possibility of using Sawdust-Cement- Gravel Mix for Residential Floor Slabs”
Researchers : Allen Antonio, Rey Baldeo and Belen Bonifacio
Adviser : Engr. Elizabeth Rodriguez Rivera
School : FEATI University
Date : March 2005
Degree : Bachelor of Science in Civil Engineering
Over the years, engineers have conjured up ways to help us adapt to our changing world more efficiently. The development of new technologies not only helps us but also the environment. It ensures that all involved benefit from this. Nowadays, recycling is becoming an issue, as well as air pollution. At the same time, the construction industry is searching for ways to develop more lightweight materials.
Fine aggregates in concrete act as small binders that shape the whole structure. It gives the mixture its texture and consistency. Sand is the primary fine aggregate being used in any concrete structure. Sawdust however is a waste byproduct of sawmills, ejected when sawing lumber. It is both lightweight and cheap, meaning that it not only helps make it possible to build more lightweight structures but can also lower the cost of structures.
Our study focuses on developing an acceptable concrete mix that can be used for residential slabs. Since most structures in residential areas require less weight than high-rise structures, it might be possible to apply certain concepts with sawdust-cement-gravel mixtures. Also, concrete slabs compose almost 40% of the structures weight since they occupy a large area. If further development is pursued, it might be possible to apply sawdust as a fine aggregate substitute for lightweight structures and maybe more.
The whole of the project tries to implicate that sawdust-cement-gravel mix has an equal advantage than the standard mix of cement-sand-gravel. Both mixed in proportions classified as Class A mix with the proportions of 1:2:4 of cement, a fine aggregate, and a coarse aggregate respectively. Two sets of sample with three sample of each were made for a total of 6 specimens to be tested. The first set of three samples consists of the sawdust-cement-gravel mix, the second set of the ordinary concrete mix. Each set were mixed and molded in the same way and with the same volume proportions. After placement in molds, both sets were left to cure for a number of days. The then curing samples will then be tested at a given period of days specified under the National Structural Code of the Philippines or NSCP ( 7, 14, and 28 days). For added data, since time is against us, we decided to minutely alter the curing processes of the sawdust-cement-gravel specimens. The seven day specimen was not cured, the fourteen day specimen was soaked, and the twenty-eight day specimen was washed with a little bit of water every morning. After each curing period assigned, each group was tested under a hydraulic press machine for compressive strength test. The results of each period presented many peculiar findings.
During curing process, a decision was made to do different curing procedures and even none. The seven day specimen, which was not cured at all, showed a high early strength yield. The fourteen day specimen, soaked in water, was lower by 100 kg/cm3 or 1,419.4 psi. the last sample, cured every morning with water, stabled at about 220 kg/cm3 or 3122.68 psi. Results indicated that the average strength of the sawdust-cement-gravel mix was about 3000 psi. which, according to NSCP standards is between 2500 psi – 3000 psi., is still in accordance with minimum safety standards. Further analysis tells us that during the hydration process of concrete, the water taken in by the sawdust particles during mixing help hydrate cement particles in places where it is impossible to cure, mainly the center. Since found that the hydration of the center of structural components like columns take most of the time in construction, sawdust particles might help lessen curing time in half and could also eliminate the need to using chemicals to cure. Henceforth, proves that sawdust can be used in concrete mixes for residential floor slabs. With regards to the weight of the two sets of samples, an equally small amount of each was made and weighed. The results were dramatic since the sawdust-cement-gravel mixture was almost half of the standard mix’s weight then again proving its lightweight property. Another observation was that every sample tested to its failing point showed wood fiber bonding at work. Faces of the sample that were supposed to fall off once cracked didn’t, instead were being held together by strands of sawdust. To make it short, rather than splitting apart like usual, it just bulked up making it a remarkable feat for a man made object that rigid. This could prove helpful during structural collapses since concrete tend to fall right off in an event of a major crack occurring.
Using sawdust rather than sand has its advantages, among these advantages were mentioned in recent studies. These included: sound insulation and reduction of about -14 dB, thermal capabilities which allowed it to retain its temperature for longer periods of time, improved flexibility cause of its synthetic wood fiber bonding replicating that of trees, and more cost efficient because it is already waste byproducts, making sawdust a good compromise to sand.
Surely the engineering field might not approve incorporating organic materials into concrete because of their decomposing property and soft molecular structure but of course technologies change as well as time. More and more developments can be developed to improve this. If a man can build a house made out of sawdust, loose soil, clay and cement then surely it is possible to be able to build improved lightweight structures with merely waste materials and organic particles. An engineer’s job is to conceptualize and not to criticize. Broadening our minds towards environmental awareness does have its pro’s and con’s. This is the idea of pushing forward towards the twenty first century of development.