Dr M.R.H. Dunstan

Chairman, Malcolm Dunstan & Associates (MD&A)

Hayford Hall, Buckfastleigh, UK



Manager of Water Resources & Energy Dept.

Nippon Koei Co., Ltd. (Japan)


Eng. R.S. Rupra/Eng. D. R. Hirani/A. Karuge

Mangat I.B. Patel (MIBP) Ltd, Consulting Engineers (Kenya)


Eng. K. Tireito

Dam Coordinator

Kenya Water Security and Climate Resilience Program

Ministry of Water and Sanitation


The proposed Mwache Multipurpose Dam is located on the Mwache River in Kwale County, 22km west of Mombasa City in the Coastal region of Kenya.  The objective of the Project is to harness the flood flows from the Mwache River Basin for domestic water supply and irrigation to Mombasa and Kwale Counties in order to mitigate the increasing variations in weather and climatic patterns.  The dam is designed as a Roller-Compacted Concrete (RCC) gravity dam capitalizing on the numerous advantages associated with the RCC technology.  It will be the first RCC Dam to be constructed in Kenya and East Africa and its construction is scheduled to commence at the beginning of 2019.  The Client of the Project is the Ministry of Water and Sanitation, Kenya. The dam and the appurtenant structures has been designed by the Association of Nippon Koei Consulting Engineers Ltd of Japan, Mangat I.B. Patel (MIBP) Ltd Consulting Engineers of Kenya and AF Consult of Switzerland with Dr. M.R.H. Dunstan of MD&A of UK as the RCC dam advisor .


Mwache Dam has an RCC volume of approximately 610, 000 m3, which is planned to be placed in 15 months.  To achieve such high rates of placement, the selection of both the RCC mix proportions and the construction methodology will have to be carefully optimized.  There was no precedent in Kenya in the use of any of the proposed materials in RCC or even concrete in the proportions envisaged for use in the Mwache RCC.  In order to obtain an economical engineering solution, a pre-bid Trial Mix Programme was considered essential.  This was to identify and assess the suitability of local materials for use in the RCC by conducting preliminary trial mixes and advise bidders on the potential suitability of these in the Tender Documents.


The paper presents the Laboratory Trial Mix Programme in detail including results achieved and the conclusions made.  It addresses sourcing, selection, processing and testing of all the potential materials, the laboratory equipment and procedures, mix design parameters and selection of suitable RCC mix proportions.  The Trial Mix Programme utilized locally-available materials which included; aggregates from a quarry downstream of the dam site, Portland cements from two factories within the dam vicinity, a natural pozzolan from a nearby deposit and retarders from local suppliers.  The only additional imported materials were two flyashes and a granulated ground blast furnace slag (GGBFS) from India and a natural pozzolan from Tanzania – all of which have been regularly imported into Kenya over a long period of time.  The materials were optimized for aggregates gradation, workability and water content, retarder dosage and cementitious materials proportions, with approximately 150 different mixes being conducted.


The results of the Trial Mix Programme produced three extremely efficient mix proportions for the different cementitious materials for use in the RCC from the ten initial mixes tried.  These mix proportions are probably among the most optimal ever used in an RCC dam in the World to date with approximately 34kg/m3 of cement + 186 kg/m3 of flyash and 50kg/m3 of cement + 170 kg/m3 of natural pozzolan respectivly for the specific mixes.  The mix proportions were incorporated into the Tender Documents for the Contractors to select their preferred choice of materials for construction of the dam.  With these mix proportions and with a carefully optimized construction methodology, it should be possible to achieve the proposed rates of placement resulting in an excellent quality for the dam structure and with the associated benefits of early Project completion.


The Authors

  1. Dr M.R.H. Dunstan obtained his first degree from Birmingham University and his PhD from Surrey University, both in the UK. He is the Chairman of Malcolm Dunstan & Associates. He has been involved with more than 125 RCC dams in over 50 different countries during the past 40 years. He is the longest serving member of the ICOLD Concrete Dam Committee and was Chairman of the Committees that drafted ICOLD Bulletins 109: Concrete dams – Control and treatment of cracks and 126:  Roller-Compacted Concrete dams – State of the art and case histories. He is the author of over 100 papers and maintains a database of all the RCC dams in the World, a summary of which is published annually in the Hydropower & Dams World Atlas and Industry Guide.


  1. J. Fukuwatari completed his Master’s degree in 1996 in Civil Engineering focusing on River and Coastal Engineering at Tohoku University, Sendai, Japan. He has worked for Nippon Koei as a Consulting Engineer for 22 years in Dam, Water Resources and River Engineering fields. He has 14 years experience in design of Domestic Dam Projects in Japan and 8 years experience in International Hydropower and Water Resources Development Projects.


  1. Eng. R. S. Rupra has undertaken a degree in Civil Engineering and a Post Graduate Diploma in Water Supply and Public Health Engineering both from Middlesex University, UK. He has over 30 years’ experience in design and supervision of multi-disciplinary teams dealing with infrastructure, water supply and sewerage projects for both urban and rural areas. He has extensive experience in Preparation of Masterplans, Feasibility Studies, Design, Supervision and Contract Management of Large Urban and Rural Water and Wastewater Projects.


  1. Eng. D. R. Hirani is a Civil Engineering graduate from South Bank Polytechnic, UK. He has over 20 years of experience in Design, Tender Documents Preparation, Construction Supervision and Contract Management of various Projects in the fields of Water Supply, Sanitation, Preparation of Master Plans and Drainage Infrastructure. He is an experienced Materials Engineer who has been responsible for Formulation and Supervision of Quality Control of Materials and Concrete on various infrastructure projects.


  1. A. Karuge possesses an Honours Degree in Civil Engineering from the University of Nairobi, Kenya. Since completing his undergraduate studies, he has been working with Mangat I.B. Patel (MIBP) Ltd, Consulting Engineers as a Civil Engineer on infrastructure projects. He has recently completed supervision of a successful RCC Trial Mix Programme for the Mwache Multipurpose Dam.


  1. Eng. K. Tireito is a Civil Engineering graduate from the University of Nairobi. He is an experienced professional engineer with more than 20 years of experience in design and construction supervision of hydraulic and civil structure projects. He has carried out all engineering activities from inception and planning of projects, through to final handing over and settlement of commercial and contractual aspects.


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