Sustainable Cement Utilization
[Enugu, Enugu State Nigeria]

From experience, laterite bricks of 330 × 150 × 150 mm have proved to be economic and can be easily laid. It is an improvement on the fired clay bricks of 250 × 150 × 100 mm because 22 bricks are required per meter square of wall as against the 33 required for fired clay bricks. Consequently, the mortar required for jointing per square meter of wall is reduced significantly (Ehinola2008).

Good laterite bricks were produced from different sites in Kano when laterite was stabilized with 3 to 7% cement . The study showed that particle size distribution, cement content, compactive effort and method of curing are factors which affect the strength of the bricks. Laterite bricks were made by the Nigerian Building and Road Research Institute (NBRRI) and used for the construction of a bungalow. From the study, NBRRI proposed the following minimum specification as requirements for laterite bricks: bulk density of 1810 kg/m3, water absorption of 12. 5%, compressive strength of 1.65 N/mm2 and durability of 6.9% with maximum cement content fixed at 5% (Ehinola 2008). Laterite stabilized with cement was used successfully to produce bricks. Three pressure ranges: 2 to 4 N/mm2, 8 to 14 N/mm2 and 6 to 20 N/mm2 which were designated low, high and hyper respectively were used in the production of bricks. With cement content of 5 to 8% and a brick size of 290 x 140 x 90 mm, compressive strength ranging from 3 to 3.5 N/mm2 was achieved using a compactive effort that ranged from 8 to 14 N/mm2. The study showed that the strength of bricks was dependent on the pressure applied during production, percentage of cement used, and the particle size distribution of the laterite.

Cement stabilized soils are usually evaluated by unconfined compressive strength (UCS) test with a minimum 7-day UCS value of 1720 kN/m2 as criterion for effective stabilization [4]. The maximum permissible cement content of 5 % was specified by NBRRI [2]. A 7-day UCS value of 1.765 N/mm2 was recommended by [1] for laterite-cement mixture when it is to be used in the production of laterite bricks.

Several researchers have reported that cement-stabilized laterite can be used in road and building construction [5-8]. Literature is scarce on the engineering properties of Ikpayongo laterite and its use in the construction industry. This objective of this study is therefore to investigate the use of cement and sand admixed with Ikpayongo laterite for brick production. The soil used in this study is a reddish brown laterite soil classified as A-2- 7(0) using AASHTO soil classification system [9] and GP by the United Soil Classification system [10]. Disturbed sample of laterite was obtained from Ikpayongo (between latitude 7°30 ׳ and 7°35 ׳ N and longitude 8°30 ׳ and ׳ 8°35 E) a distance of 22 km from Makurdi, the capital of Benue State of Nigeria, along Makurdi-Otukpo road. Sand used for the test was obtained from River Benue in Makurdi. Ordinary Portland cement (Dangote cement produced by Benue Cement company in Gboko) was purchased from the open market and used in this study as the stabilizing agent while portable tap water was employed in the laboratory tests conducted.

Compaction was carried out at the West African standard (WAS) energy level. Optimum moisture content obtained from the compaction test was used in moulding ultimate compression strength specimen. UCS test was performed on laterite mixed with sand and cement in accordance with [11] and [12] for the natural and stabilized materials respectively.

The soil-sand-cement mixtures for specimens were prepared by thoroughly mixing predetermined quantities of air-dried lateritic soil, sand and Portland cement until a uniform colour was obtained. Thereafter an amount of water lxviii necessary to give the required moisture content was added to the dry mixtures before compaction at the energy level of the SP and WAS. Specimens for UCS tests were cured in sealed plastic bags for 7 and 28 days. The plastic bags were sealed to prevent loss of moisture by evaporation.

Based on the 7-day ultimate compression strength results, laterite bricks were produced using soil-sand-cement mixtures with 0 and 45% sand content and 0, 3, 6, and 9 cement content. Laterite and sand were air dried for 24 hours before passing them through 10 mm sieve. Particles passing through the sieve were used for brick production. The required proportions of sand, laterite and cement were mixed manually on a clean and firm platform using a shovel. Cement and sand were mixed together then laterite was added to the mixture. Thereafter water was added and mixing continued until a homogeneous mix was obtained. Trial mix results showed that a water to cement ratio of 0.56 gave the best result, hence this ratio was used for brick production.

The damp mix was poured into the twin steel moulds of a locally fabricated manual press machine, after lubrication with water/oil. A wooden pallet was lxix placed at the bottom of the mould to allow easy removal of the bricks after being pressed. The damp mix was poured into the mould with the aid of a shovel, while tamping was carried out with a 20 mm diameter rod. A hinged mould lid weighing 15 kg was dropped six times from a height of 30 cm onto the exposed top of the mixture in the mould. This is equivalent to a pressure of 3 N/mm2. The hinged lid was closed at the top of the mould and locked with bolts and nuts to allow for effective pressing from the bottom of the mould, with the aid of the lever arm. The pressed blocks (two in number) were ejected using the single lever arm, thereafter the lid was opened and the bricks removed. The fresh bricks on the wooden pallet were carried carefully to a shade and covered with polythene bags to avoid loss of moisture. The bricks were covered with tarpaulin and left to cure for 7 and 28 days. Ten bricks, made for each sand-cement mixture, were immersed in water for 24 hours before subjecting them to compressive test at 7 and 28 days using an ELE compression machine (Agbede 2002).

The above figure shows the curves of grain size distribution for sand, laterite and laterite mixed with sand. The distribution curve for the pure laterite is stepped, an indication of a poorly graded sample, arising from lack of some intermittent particle sizes in the ranges of 1.18 mm, 600 μm lxx and 300 μm. It has specific gravity of 3.10. The curve for pure sand is a smooth curve. Its coefficient of uniformity and curvature are 3.31 and 0.80 respectively. The sand can be classified is poorly graded; its specific gravity is 2.69 and it belongs to zone 2 of [13] sand grading zone. The distribution curve for laterite admixed with sand and cement is smooth implying that the poorly graded laterite soil was greatly improved by the addition of sand (Cu reduced from 47.3 to 13.82). Specific gravity of 2.95 and 2.90 was obtained when laterite was admixed with 30 and 45% sand respectively. The addition of 45% sand to the laterite increased the coarse sand component of the laterite from 30% to 53% while medium sand component or the percentage passing through the 600 μm sieve increased from 20% for natural laterite to 40% when admixed with 45% sand. Sand addition increased the sand component of the laterite thereby correcting the deficient intermittent particle size ranges in the natural laterite.

2.7.4 Compaction Characteristics

The effect of cement and sand content on the maximum dry density (MDD) of lateritic soil at the WAS energy level is shown in Figure 2. Generally, MDD increased with the addition of sand alone, cement and their respective combinations. MDD increased from 1.88 Mg/m3 for the natural lxxi laterite to a peak value of 2.00 Mg/m3 at a sand-cement mixture of 45% sand and 9 % cement. Increase in MDD could be attributed to voids of the natural lateritic soil being filled with sand size particles and cement with a higher specific gravity of 3.15.

The variation of optimum moisture content of stabilized lateritic soil with cement and sand content at WAS compactive effort is shown in Figure 3. Optimum moisture content decreased with sand content but increased with cement and cement-sand mixture. Increase in OMC with the use of cement is probably due to water required for the hydration of cement. Decrease in OMC with the use of sand can be attributed to the reduction in the surface area of the fine component of laterite by the increase in sand size particles. Compaction test was carried out to identify the moisture content that will be used for moulding of UCS specimens for the different combinations.

2.7.5 Shear Strength Characteristics

Figures 4 and 5 show the variation of UCS with cement for the soil-sandcement mixtures at the WAS energy level for 7 and 28 days respectively. Figure 4 shows that 7-day UCS value increased with sand and cement up to a sand content of 45%, it however decreased at 60% sand content. A lxxii similar trend could be observed in Figure 5 for the UCS at 28 days. Based on the peak strength exhibited at 45% sand content for UCS specimens at 7 and 28 days, natural laterite and laterite mixed with 45% sand and cement (3, 6 and 9%} were used in the production of laterite bricks.

Using the optimum cement content of 5% and a 28 day compressive strength of 1.65 N/mm2 for bricks as the criteria, compressive strength test results show that soil-cement mixtures did not satisfy both requirements. The requirement was met at 9% cement, which is far above the economic cement content. For a laterite-cement mixture of 45% sand and 5% cement, a compressive strength of 1.80 N/mm2 (obtained by interpolation) was obtained. This value met the requirements.

When the cement content was slightly increased to 6%, laterite-sandcement mixture of 6% cement and 45% sand met the strength of 2.0 N/mm2 proposed by where bricks are to be used for one-storey building. It can be observed that the pressure of 3 N/mm2 applied in the moulding of bricks in this study fell into the range of low pressure used by [3]. If the higher-pressure ranges were used in moulding the bricks, the expected compressive strength results would have been higher than the values lxxiii obtained in this study. Reported such increase in compressive strength with compactive effort.