A STUDY ON PERFORMANCE EVALUATION OF STABILIZED EXPANSIVE CLAY SOIL WITH SORGHUM HUSK ASH CEMENT BLENDS IN NKONDI, KENYA

Abstract

Expansive soils, which are widespread globally, are a major cause of structural damage such as cracks in buildings, roads, and pavements. Stabilizing these soils is essential to minimize their plasticity, shrinkage or swelling potential, and thus improve their strength and durability. One of the most common approaches to soil stabilization is chemical treatment, where chemical additives are mixed with the soil to trigger a chemical reaction. Ordinary Portland Cement (OPC) has been the most widely used additive for stabilizing expansive soils. However, its high cost makes it less accessible to low-income populations, particularly in developing nations. Additionally, the production of OPC is a major environmental concern, contributing 5-8% of the global human-made carbon (IV) oxide emissions. The study examined the performance of expansive clay soil stabilized with sorghum husk ash (SHA) blended cement. Soil samples were collected from Nkondi ward in Tharaka Nithi County, Kenya at varying depths of 0–30, 30–60, and 60–90 cm, while sorghum husks were obtained from Mwanyani location in the same ward. The clay soil was characterized before and after calcination to establish mineralogical and chemical properties. The clay soil samples were calcined at a temperature of 700 oC for 2 hours in a furnace to transform the unreactive kaolinite mineral into metakaolin, which is the reactive phase. The sorghum husks samples were burnt in a furnace to produce the ash at a temperature of 600, 700 and 800 oC for 2hours each. Clinker, limestone, and gypsum were sourced commercially sourced from Ndovu cement company. Sorghum Husk Ash and calcined clay was incorporated in cement by substituting clinker from 40 to 80% in three samples labelled as S2, S3 and S4. S2 was prepared by combining 80% clinker, 15% limestone and 5% gypsum totaling to 100%. The rest of the samples were prepared by reducing clinker to 40% with varying proportions of calcined clay and SHA, while gypsum and limestone contents were fixed at 5% and 15% respectively totaling to 100%. S1 soil sample was the unstabilized clay soil. The stabilized soils were tested for compaction, Atterberg limits, linear shrinkage, particle size distribution, and California Bearing Ratio (CBR). X-ray diffraction (XRD) results indicated that raw clay samples contained kaolinite, quartz, and feldspars. Calcination reduced kaolinite phases, with increased amorphous aluminosilicate phases observed. X-ray fluorescence (XRF) analysis of calcined clay showed an increase in silica and alumina oxides, enhancing pozzolanic potential. The chemical composition of sorghum husk ash burnt at 700 oC for 2 hours showed silica at 68.93%, alumina at 3.3%, and ferric oxide at 3.85%, giving a combined total of 76.08%, which satisfied the pozzolanic criteria. Grading was done by particle size distribution and the results showed that 4.0% of soil was retained on the 10 mm sieve, 4.7% on the 5.0 mm sieve, 3.5% on the 2.0 mm sieve, 1.9% on the 1.0 mm sieve, 5.5% on the 0.425 mm sieve, and 17.8% on the 0.075 mm sieve, with 62.6% passing the pan. Proctor compaction gave a maximum dry density of 1.601 gcm-3 and optimum moisture content of 20.8%. The natural moisture content was at 11.6%. California Bearing Ratio (CBR) results at 2.54 mm penetration were as follows; S1 recorded 21.2% at 10 blows, 64.8% at 30 blows, and 80.1% at 65 blows. S2 yielded 23.8%, 77.0%, and 90.6% under similar conditions. S3 exhibited 15.5, 26.0, and 45.9% while swell potentials reduced to 3.69, 0.01, 0.33, and 0.45% respectively. Atterberg limit tests showed liquid limits of 48.8 (S1), 44.3 (S2), 46.4 (S3), and 45.6% (S4), with constant plastic limit of 28% across samples, producing plasticity indices of 16, 18, and 17% respectively. Linear shrinkage values were 14% for S1, 9% for S2, 10% for S3, and 11% for S4. This study aimed to develop an eco-friendly construction material by increasing soil strength using sorghum husk ash