Strength and durability aspects of calcined kaolin-blended Portland cement mortar and concrete D.D. Vu a,1 , P. Stroeven b, * , V.B. Bui a,1 a Hanoi University of Civil Engineering, Hanoi, Vietnam, 5 Giai phong Road, Hanoi, Viet Nam b Faculty of Civil Engineering and Geosciences, Delft University of Technology, P.O. Box 5048, 2600 GA Delft, The Netherlands Abstract Economicandsustainabilityargumentsrequirecarefullyassessingthepotentialitiesofindigenousresourcesfortheproductionof mortarandconcretefortheconstructionindustry.InVietnam,signi®canteortsshouldbebestowedonurbandevelopment,coastal protectionandharbourconstructionworks.InajointVietnamese-Dutchco-operationprogram,thepracticaluseforthispurposeof relevant resources in Northern Vietnam is assessed experimentally. This paper concentrates on kaolin, which is widely available in this region. The key issues this paper is dealing with are the eects of partial replacement of Portland cement by calcined kaolin in mortar and concrete on compressive strength as well as on durability characteristics of mortar and concrete mixes pertinent to the coastal environment. Workability measures are also mentioned. Data are therefore presented on compressive strength development overamaximumcuringperiodof180daysofmixesinwhichthewatertobinderratiowasvariedbetween0.40and0.53.Moreover, partial replacement was considered in the range from 0% to 30% by weight. The results of this study render possible the assessment of optimum replacement percentages of Portland cement by calcined kaolin, and the associated strength gain. Additionally, this paper reports on the performance aspects of similarly blended mortar and concrete specimens stored for a period of one year in a low concentration of a sodium sulfate solution. It could be concluded that a strength gain due to blending will be accompanied by improved durability in this environment. Ó 2001 Published by Elsevier Science Ltd. Keywords: Blending; Compressive strength; Concrete; Durability; Kaolin; Pozzolan; Mortar; Sulfate resistance 1. Introduction In many countries around the world, kaolin and clay are used for producing active pozzolanic admixtures. These pozzolanic admixtures are used for reducing the Portland cement content in mortar and concrete pro- duction [1±4]. The positive eects exerted by such po- zzolanic admixtures on properties of Portland cement mortar and concrete have been emphasized in many studies [5±7]. In addition to a strength gain, it was shown that such admixtures could improve the sulfate resistance of the Portland cement mortar and concrete [8,9]. However, what can be expected in a speci®c situ- ation will depend on the mineralogical and chemical composition of the mineral admixture. For the present purpose interesting indigenous re- sources as alumina-rich clays and kaolin are abundant and widespread through many districts in Northern Vietnam. A limited survey of such mineral resources employed in Northern Vietnam is presented in Table 1. This study therefore focuses on the degree to which kaolin could replace Portland cement in mortar and concrete production in Northern Vietnam. The key is- sues in emphasizing the potentialities of kaolin for this purpose are the compressive strength and the durability in a low-concentration sodium sulfate solution. On the strength testing of kaolin-blended pastes, mortars and concretes has been reported earlier. For more details, such as on the characterization of the kaolin as a proper pozzolanic material, the reader is referred to these publications [3,4,10]. For a more elaborate report on the durability aspects, also encompassing ¯exural testing and a more concentrated sulfate solution environment, see [10]. The experiments are continued in Vietnam, particularly focusing on concrete. The results of this investigation will be reviewed later. Cement & Concrete Composites 23 2001) 471±478 www.elsevier.com/locate/cemconcomp * Corresponding author. Tel.: +31-015-278-4035; fax: +31-015-261- 1465. E-mail address: p.stroeven@ct.tudelft.nl P. Stroeven). 1 Fax: + 84-4-869-1684 0958-9465/01/$ - see front matter Ó 2001 Published by Elsevier Science Ltd. PII:S0958-946500)00091-3