Sandcrete blocks are prismatic units manufactured from lean (sand-cement) mortar mixes and are the predominant walling materials used in buildings in Nigeria and other countries. Although the blocks are preferred to other similar walling material such as bricks and concrete blocks due to the availability of the dominant material (sand) in the country and the ease of manufacture, the material is known to have several drawbacks: it has a low compressive strength which could be a factor for structural failure in buildings. Apart from the compressive strength, little is known about the other strength and permeation properties of the material. Thirdly, little research has been conducted into the influence of water-cement ratio which is known to wield a strong influence on the strength and permeation properties of cementitious materials. On the basis of a thorough review of the literature, a detailed experimental programme was designed and carried out in Nigeria on the factors that influence the strength and permeation properties of the material using over 10 destructive test methods. Over 1500 sandcrete blocks were moulded and tested. The literature review also indicated that lack of quality control in the Nigeria sandcrete blocks manufacturing industry which accounts for the poor quality of the material in the country. The results of the experimental programme indicate that with the right constituent materials,   manufacturing   and   curing   processes,   it   is   possible   to   improve   the compressive strength of sandcrete blocks to over 7.0N/mm2 (the minimum specfied by the British Standards) with a lean mix of 1:12 cement/sand ratio. The compressive strength of the material was found to have a strong relationship with other strength properties of the material and could therefore be used as the main criterion for determining its quality. The inclusion of quarry dust and coarse aggregate (sharp sand) significantly improved the strength and permeation properties of the blocks. Compared with normal concrete, sandcrete; was found to have a relatively high permeability. Through this study, a data base on several strength and permeation properties has been developed which can assist engineers to estimate these properties. Finally recommendations were made on ways of improving the quality of sandcrete blocks in the country.
CHAPTER ONE
INTRODUCTION
1.1.            Research Background
Sandcrete blocks are produced from a lean mix of Portland cement, natural sand and water and are the main masonry unit used in the urban and peri-urban areas of Nigeria, West Africa and many parts of the developing world. Unlike other masonry units such as concrete blocks and burn bricks which are used in other civil engineering infrastructure, they are predominantly used as walling units in the construction of shelter: both as external cladding and for partitions. They have an appeal to the construction industry due mainly to its ease of manufacture and the widespread availability of the main constituent material (sand).
A number of studies including the project National de Recherche/Development (Sablocrete) (1994) carried out in France have designated sandcrete as a member of a family of concretes, which can be used when environmental and economic constrictions restrict the use of coarse aggregate. This project carried out in France (Sablocrete) revealed the economical and mechanical advantages of this material and showed typical applications in public works and building.
In researching into the properties of sandcrete blocks as defined by this study, one is faced with a delimma, little material exists in the technical literature on certain properties of sandcrete blocks such as its durability, tensile, transverse and flexural strength and the value of elastic constants. One way of overcoming this problem is to compare sandcrete with some of its closest relatives such as concrete and mortar. In fact as a material, sandcrete can be considered as a form of zero-slump concrete or mortar. This three materials share many common characteristics even though their properties diverge at a point. For this reason, extensive references are made in this study to concrete and mortar.