International Journal of Scientific and Research Publications, Volume 11, Issue 6, June 2021 423 ISSN 2250-3153 This publication is licensed under Creative Commons Attribution CC BY. http://dx.doi.org/10.29322/IJSRP.11.06.2021.p11457 www.ijsrp.org Optimisation Model for Proportioning the Aggregates of High Strength Laterised Concrete Dr. Udeme Hanson Iron * and Professor Dahunsi, Bamidele I.O. ** * Lecturer, Department of Civil Engineering, Faculty of Engineering, University of Uyo, Nigeria ** Professor, Department of Civil Engineering, Faculty of Technology, University of Ibadan, Nigeria DOI: 10.29322/IJSRP.11.06.2021.p11457 http://dx.doi.org/10.29322/IJSRP.11.06.2021.p11457 Abstract- Laterite, a typically red or reddish brown soil found in abundance in the tropics has been used to partially or wholly replace sand in concrete. Resulting laterised concretes are generally known to exhibit low strengths. In this study, the production of high strength laterised concretes using superplasticiser was experimented. Scheffe’s simplex theory based on (6,2) simplex lattice was used to optimize the mix proportions for the crushing strength of high strength laterised concrete produced using Conplast SP 430 superplasticiser (a sulphonated naphthalene formaldehyde admixture). Mathematical models were developed for the mix proportioning of high strength laterised concrete. All strengths predicted by the developed mathematical model are in good agreement with their corresponding experimentally observed values. Using the model, the mix proportions for any targeted strength of hardened concrete is easily evaluated with the help of the computer programme. A computer programme written in Q-BASIC language is also provided for speedy generation of the mix proportions for the targeted strength. Index Terms- Crushing strength, Laterized concrete, Optimisation, Simplex lattice, Superplasticiser. I. INTRODUCTION aterised concrete has found immense use of recent for the construction of low-cost buildings. The use of this material is known to reduce the cost of structures due to the abundance of laterite within the tropics and sub tropics (Udoeyo et al, 2006). Studies on the usage of this material have shown very encouraging results (Orangun 1981). Although used, its usage has hitherto been limited to structures of lower strengths. Moreover, in most previous studies on laterised concretes, the traditional mix design methods with its cumbersome nature were utilized. The need to produce laterised concretes of higher strengths and also eliminate the errors and cumbersome nature of the traditional mix design methods informed the will to embark on this study in order to develop an optimization model for accurate and effective proportioning of high strength laterised concretes. The strength of concrete is a function of the proportions of the ingredients that make up the concrete. The task of accurate proportioning still remains a problem to concreters. Eliminating this problem is the focus of this study. The crushing strength (f c ), which is the most desired and convenient to measure quality of hardened concrete, is optimized in this study. It is evaluated using: f c = P/A [1] Where P is the maximum crushing load at failure and A is the cross sectional area of the specimen (cube). II. MATERIALS AND METHODS 1.1 Materials Materials used in this study were water, cement, sand, laterite, coarse granite aggregate, and Conplast SP 430 superplasticizer. Laterite: The laterite was obtained from burrow pits in Uyo, Akwa Ibom State of Nigeria. Its specific gravity was 2.62 and it was a zone 3 aggregate according to BS 882:1992 classification. Its elemental contents were analysed at the Ministry of Science and Technology laboratory in Akwa Ibom State and presented in Table 1. Its fineness modulus and coefficient of uniformity were 2.33 and 2.40 respectively. Sand: The sand was obtained from Ikpa River in Uyo and prepared according to BS 882 – 103:1992 requirements. It had a specific gravity of 2.65, fineness modulus of 2.37 and coefficient of uniformity of 2.83. It was a zone 2 aggregate with reference to BS 882 – 103:1992 grading system. The particle size distribution of the sand and laterite are shown in figure 1. Coarse aggregate: The coarse aggregate was coarse granite stones obtained from Akamkpa in Cross River State, Nigeria. It had a specific gravity of 2.71, impact value of 13.15% and crushing value of 21.43 with a size ranging between 10mm and 20mm. L