SILICA FUME CONCRETE STUDIES- A PROGRESS REPORT April 1985 Engineering and Research Center U. S. Department of the Interior Bureau of Reclamation \ Division of Research and L Laboratory Services \Concrete and Structural Branch LIBRA Jlll29'f April 1985 Bureau of Reclar on Denver, Col~ri Silica Fume Concrete Studies - A Progress Report 6. PERFORMING ORGANIZATION CODE 7. AUTHOR(SI 8. PERFORMING ORGANIZATION REPORT NO. Fred E. Causey GR-85-3 I 9. PERFORMING ORGANIZATION NAME AND ADDRESS 110. WORK UNIT NO. Bureau of Reclamation Engineering and Research Center 11. CONTRACT OR GRANT NO. Denver, CO 80225 0 13. TYPE OF REPORT AND PERIOD COVERED 12. SPONSORING AGENCY NAME AND ADDRESS 14. SPONSORING AGENCY CODE DlBR I 15. SUPPLEMENTARY NOTES Microfiche and/or hard copy available at the Engineering and Research Center, Denver, Colorado Editor: RNW (c) Is. ABSTRACT Research in the late 1960's showed that the use of silica fume (microsilica) as a partial replacement for cement in concrete mixes produced a dense concrete with properties su- perior to those of ordinary portland cement concrete. These properties indicated silica fume concrete would have a number of advantages when used for the repair of concrete structures. Tests were performed on some 40 mixes made using silica fume as a replacement for cement in quantities of 15, 20, and 30 percent. The results of this research program indicated that the following benefits might be achieved with silica fume portland cement concrete: increased strength, increased freezing and thaw- ing resistance, improved mix consistency, reduced bleeding, and increased abrasion resist- ance. Good concreting practices, especially during curing, must be maintained when using silica fume or the following may result: increased plastic shrinkage, increased long-term shrinkage, increased color variations, increased handling and finishing (workability) problems, increased placing costs, and lower strength. 17. KEY WORDS AND DOCUMENT ANALYSIS 0. DESCRIPTORS-- "silica fume/ cements/ portland cement concrete/ 'concrete mixes/ concrete/ "concrete additives/ pozzolanic materials/ concrete tests/ compressive strength/ tensile strength/ repair materials/ construction materials/ bleeding/ abrasion resistance/ workability/ shrinkage b. IDENTIFIERS-- Waterways Experiment Station c. COSATl Field/Group 13C COWRR: 1303 SR IM: 18. DISTRIBUTION STATEMENT 19. SECURITY CLASS kl. NO. OF PAGE (THIS REPORT) UNCLASSIFIED 19 20. SECURITY CLASS 22. PRICE (THIS PAGE) UNCLASSIFIED SILICA FUME CONCRETE STUDIES - A PROGRESS REPORT by Fred E. Causey Concrete and Structural Branch Division of Research and Laboratory Services Engineering and Research Center Denver, Colorado April 1985 UNITED STATES DEPARTMENT OF THE INTERIOR .k BUREAU OF RECLAMATION As the Nation's principal conservation agency, the Department of the Interior has responsibility for most of our nationally owned public lands and natural resources. This includes fostering the wisest use of our land and water resources, protecting our fish and wildlife, preserv- ing the environmental and cultural values of our national parks and historical places, and providing for the enjoyment of life through out- door recreation. The Department assesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also has a major respon- sibility for American Indian reservation communities and for people who live in Island Territories under U.S. Administration. The information contained in this report regarding commercial prod- ucts or firms may not be used for advertising or promotional purposes and is not to be construed as an endorsement of any product or firm by the Bureau of Reclamation. " CONTENTS Page Introduction ............... Summary and conclusions............................................................................................................ 2 Mix design development.............................................................................................................. 2 Properties.. .. .. .. ...... ..................... .. .... ... ....... ........ 5 Compressive strength testing,"" modulus of elasticity, """and Poisson's ratio 5 Silica fume mix of 30 percent..............................................................................................."""'"'''''''''''''''''''''''''''' 5 Silica fume mixes of 20 and 15 percent................................................................................. 5 Tensile tests ... 6 Shear bond tests..................................................................................................................... 6 Thermal tests . 6 Abrasion tests......................................................................................................................... 7 Shrinkage ........... 7 Durability tests........................................................................................................................ 7 Bibliography ,... 7 TABLES Table 1 Silica fume composition.................................................................................................. 9 2 Silica fume concrete mix design....................................................................................... 10 3 Aggregate gradation....................................................................................................... 12 4 Compressive strength, modulus of elasticity, and Poisson' s ratio....................................... 12 5 Tensile strength tests..................................................................................................... 12 6 Shear bond tests on 15 percent silica fume, non-air-entrained concrete.............................. 13 7 Thermal tests on 15 percent silica fume, non-air-entrained concrete.................................. 13 8 Concrete mix design for conventional concrete abrasion test specimen.............................. 13 9 Abrasion tests............................................................................................................... 13 10 Freezing and thawing tests.............................................................................................. 14 FIGURES Figure Typical compressive stress-strain curve for a 20-percent silica fume, non-air-entrained specimen . ... ..... .. .,... .. .. .. .... ..... 15 2 Typical direct tensile"""'" stress-strain curve"'" for a""'"30-percent""" silica fume, air-entrained "" specimen. .....,... .. 16 3 The 20-percent silica"'" fume, non-air-entrained"'" specimen"'" after"'" 72 hours""'" in the Waterways Experiment Station abrasion-erosion equipment........................................... 17 4 Cure shrinkage for a 30-percent silica fume mix................................................................ 18 5 Cure shrinkage for a 30-percent silica fume mix with curing compound.............................. 19 Hi INTRODUCTION In recent years, there has been considerable interest in improving the properties of concrete by incorporating various pozzolanic materials in the concrete mix. One of these materials, silica fume, has been receiving much attention because of its favorable contributions to portland cement concrete properties. Silica fume is a byproduct from the production of ferrosilicon and silicon metal in an electric arc furnace. This byproduct is usually composed of more than 90 percent silicon dioxide and may contain traces of other oxides, depending on the furnace charge and the silicon metal being produced. Initial investigations ofthe use of silica fume in concrete were conducted in the 1-950's and 1960's, but most of the actual mix design work and the use of silica fume in concrete were not started until 1969. The Norwegians have been the most active in the development of silica fume concrete. Silica fume particles are very small. Malhotra [1]* gives a fineness of 20 000 m2jkg. Chatterji [2] points out: "From the specific gravities and specific surfaces of silica fumes and portland cement, it can be shown that around each grain of portland cement there are about 100 000 grains of silica-fume." In much of the literature, test results of silica fume concrete have been compared as though silica fume is of uniform composition. However, producers of silica fume and reports on silica fume concrete state that the Si02 (silicon dioxide) content in silica fume varies from plant to plant (table 1). It is important to work with a material that has a consistent chemical composition, fineness, and reactivity because variations in compositions may cause problems that affect the mix design, production process, and control procedures. Composition variations also can affect the degree of compactibility, the amount of water required, the workability of the mix, and the color of the concrete. How silica fume reacts in portland cement concrete is still being studied, and the chemistry of the reaction is still being debated. Nevertheless, it is safe to say that proper proportioning of silica fume, portland cement, HRWRA (high range water-reducing admixture). and concrete aggregate produces a concrete with excellent properties. Compressive strengths over 15 000 Ibjin2 (103 MPa) have been reported as well as excellent abrasion and freezing and thawing resistance. .Numbers in brackets refer to the Bibliography. 1 Because of favorable reports on silica fume concrete, a study of its properties was started in July 1983. With the thought of using silica fume concrete as a repair material (overlays and patches), a mix design was developed using