Properties of concrete incorporating high volumes of class F fly ash and san fibers $ Rafat Siddique* Department of Civil Engineering and Mechanics, UWM Center for By-Products Utilization, College of Engineering and Applied Science, University of Wisconsin-Milwaukee, P.O. Box 784, Milwaukee, WI 53201, USA Received 20 September 2002; accepted 19 May 2003 Abstract The results of an experimental investigation to study the effects of replacement of cement (by mass) with three percentages of fly ash and the effects of addition of natural san fibers on the slump, Vebe time, compressive strength, splitting tensile strength, flexural strength and impact strength of fly ash concrete are presented. San fibers belong to the category of ‘‘natural bast fibers.’’ It is also known as ‘‘sunn hemp.’’ Its scientific (botanical) name is Crotalaria juncea. It is mostly grown in the Indian subcontinent, Brazil, eastern and southern Africa and some parts of the United States (Hawaii and Florida). A control mixture of proportions 1:1.4:2.19 with W/Cm of 0.47 and superplasticizer/ cementitious ratio of 0.015 was designed. Cement was replaced with three percentages (35%, 45% and 55%) of class F fly ash. Three percentages of san fibers (0.25%, 0.50% and 0.75%) having 25-mm length were used. The test results indicated that the replacement of cement with fly ash increased the workability (slump and Vebe time), decreased compressive strength, splitting tensile strength and flexural strength and had no significant effect on the impact strength of plain (control) concrete. Addition of san fibers reduced the workability, did not significantly affect the compressive strength, increased the splitting tensile strength and flexural strength and tremendously enhanced the impact strength of fly ash concrete as the percentage of fibers increased. D 2003 Elsevier Ltd. All rights reserved. Keywords: Concrete; San fibers; Fly ash; Mechanical properties 1. Introduction Cement is the most costly and energy-intensive compo- nent of concrete. The unit cost of concrete can be reduced by partial replacement of cement with fly ash. The disposal of fly ash is one of the major issues for environmentalists, as dumping of fly ash as waste material causes severe envi- ronmental problems. The utilization of fly ash instead of dumping it as a waste material can be partly used on economic grounds as pozzolana for partial replacement of cement and partly because of its beneficial effects of lower water demand for similar workability, reduced bleeding and lower evolution of heat. It has been used particularly in mass concrete applications and large volume placement to control expansion due to heat of hydration and also helps in reducing cracking at early ages. The proportion of fly ash used as a cementitious com- ponent in concrete depends on several factors. The design strength and workability of concrete, water demand and relative cost of fly ash compared with cement are particu- larly important in mixture proportioning of concrete. One of the major developments in the area of fly ash utilization in concrete has been the technology of high-performance, high-volume fly ash concrete by Malhotra and Ramezanian- pour [1] and Malhotra [2]. High fly ash concretes with fly ash/cementitious ratio up to 75% (by mass) and an aggre- gate/cement ratio of 6 have compressive and flexural strengths that are more than adequate for lean concrete base or subbase application in pavement structure [3]. Concrete containing 50% replacement by mass of class F fly ash can be designed to have 1- and 28-day cube strengths of 20 and 60 MPa, respectively [4]. High-volume fly ash concrete has adequate early-age and later-age strength developments and considerably lower temperature rise, and its applications should have a water content of not less than 115 kg/m 3 and a 0008-8846/$ – see front matter D 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0008-8846(03)00192-3 $ This is the modified version of the paper published in the Supplementary Proceedings of Third CANMET/ACI International Sympo- sium on ‘‘Sustainable Development of Cement and Concrete,’’ San Francisco, CA, September 16 – 19, 2001. * Tel.: +1-414-229-4105; fax: +1-414-229-6958. E-mail address: siddique _ 66@yahoo.com (R. Siddique). CEMCON-02413 Cement and Concrete Research xx (2003) xxx – xxx