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REPORT ON CHEMICAL ADMIXTURES FOR CONCRETE
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ATTACHMENT ACI 212 3R 10 REPORT ON CHEMICAL ADMIXTURES FOR CONCRETE. ACI 212 3R 10,Report on Chemical Admixtures,for Concrete. Reported by ACI Committee 212,CHAPTER 15 PERMEABILITY REDUCING ADMIXTURES. 46 REPORT ON CHEMICAL ADMIXTURES FOR CONCRETE ACI 212 3R 10. mortar bar tests ASTM C1260 or ASTM C1567 For water ingress under actual service conditions This definition. testing in ASTM C1293 the limit is generally less than is not technically correct as it could refer to either permeability. 0 04 at 2 years or capillary absorption as defined previously however. In Fig 14 1 the LiOH and LiNO3 were both added at the permeability is commonly understood to refer to any passage. 100 dose note the greater effectiveness of the LiNO3 As a of water through concrete For the purpose of this chapter. demonstration of the high reactivity level of this aggregate admixtures intended to reduce water ingress will be split into. note that levels of Class F fly ash up to 30 were not sufficient two subcategories PRAs for concrete exposed to nonhydrostatic. to control the expansion of this aggregate Often 30 of Class F conditions PRAN and PRAs for concrete exposed to. fly ash will suppress expansion of most aggregates used for hydrostatic conditions PRAH In addition to permeability. concrete manufacture in North America The 100 dose of reduction some PRAs may exhibit other beneficial character. LiNO3 will not always be sufficient for every aggregate istics such as reduced drying shrinkage Munn et al 2003. Performance testing is recommended when using Li based lowered chloride ion penetration Munn et al 2003 enhanced. admixtures freezing and thawing resistance Ramachandran 1995 Rixom. and Mailvaganam 1999 and enhanced autogenous sealing. 14 7 Storage Skoglund and Johansson 2003 Kubal 2000. Lithium admixtures should be stored in strict accordance. with the manufacturer s recommendations Most admixtures 15 2 Materials. are not damaged by freezing The manufacturer s instructions Depending on the manufacturer PRAs include but are not. should be followed regarding the effects of freezing the limited to materials from one or more chemical families. product An admixture stored beyond its recommended shelf They are as follows. life should be retested before use Hydrophobic or water repellent chemicals are the. largest group and include materials based on soaps and. CHAPTER 15 PERMEABILITY REDUCING long chain fatty acid derivatives vegetable oils. ADMIXTURES tallows soya based materials and greases and. 15 1 Introduction petroleum mineral oil paraffin waxes and bitumen. While it is generally accepted that well proportioned and emulsions These materials provide a water repellent. properly cured concrete produced using a low w cm will layer along pores in the concrete but the pores remain. result in a finished product with good durability and low physically open. permeability no concrete structure is absolutely waterproof Finely divided solids include materials such as inert. or bottle tight Perkins 1986 Concrete is a porous mate and chemically active fillers talc bentonite silicious. rial and water can penetrate concrete through pores and powders clay hydrocarbon resins and coal tar pitches. microcracks due to capillary absorption often referred to as and chemically active fillers lime silicates and colloidal. wicking or due to hydrostatic pressure Capillary absorption is silica Fine solids act as densifiers and physically restrict. the movement of water through the small pores in concrete the passage of water through the pores Some authors. in the absence of an externally applied hydraulic head and is include SCMs in this category as well and. the result of surface interactions between the water and the Crystalline materials consist of proprietary active. pore wall The permeability of concrete is the movement of chemicals provided in a carrier of cement and sand. water due to a pressure gradient such as water in contact The hydrophilic nature of these materials causes them. with a concrete structure installed underground In some to increase the density of calcium silicate hydrate. cases porosity may be exacerbated by external factors such CHS and or generate pore blocking deposits that. as incomplete consolidation and curing which may ultimately resist water penetration. lead to reduced durability The addition of supplementary These families of materials are used alone or in combination. cementing materials SCMs into concrete mixtures has been to give varying ranges of performance. gaining acceptance with respect to improving durability and Perhaps the most widely used PRANs for damproofing. reducing permeability Munn et al 2005 In addition a class protection under nonhydrostatic conditions are hydrophobic. of materials referred to as permeability reducing admixtures materials based on salts of fatty acids Calcium ammonium. PRAs have been developed to improve concrete durability and butyl stearates are perhaps the most common as well as. through controlling water and moisture movement Roy and oleic caprylic and capric derivatives Ramachandran 1995. Northwood 1999 as well as by reducing chloride ion ingress Rixom and Mailvaganam 1999 According to Ramachadran. Munn et al 2003 and permeability Munn et al 2005 1995 these materials react according to the following reaction. PRAs encompass a range of materials with variances in. performance Ca OH 2 RCOOH Ca COOR H2O, Although PRAs are traditionally subcategorized as calcium hydroxide stearate admixture insoluble calcium water. damproofing and waterproofing admixtures Ramachandran lime stearate. 1995 ACI 212 3R Aldred 1989 perhaps it is too absolute. to state that concrete can be made waterproof Further The insoluble stearate created by the reaction between the. complicating matters many concrete professionals use the admixture and the lime forms a hydrophobic layer on the. term permeability to mean the resistance of concrete to walls of the concrete pores Waxes and bituminous emulsions. American Concrete Institute Copyrighted Material www concrete org. REPORT ON CHEMICAL ADMIXTURES FOR CONCRETE ACI 212 3R 10 47. are other materials that can deposit hydrophobic particles in. the concrete pores although there is no chemical reaction. involved in that process Hydrophobic admixtures are effective. at reducing the capillary absorption and chloride ingress of. concrete under nonhydrostatic conditions as shown in Fig 15 1. and 15 2 respectively Aldred et al 2001 Civjan and. Crellin 2008, In theory the hydrophobically modified concrete should be. able to resist water up to 13 12 ft 4 m head pressure. Ramachandran 1995 and even up to 45 92 ft 14 m Aldred. et al 2001 but after accounting for the fact that the material Fig 15 1 Water absorption for ordinary portland cement. OPC concrete with hydrophobic ingredient BS EN 1881. is unlikely to completely and uniformly coat all pores plus the. 122 with an age of 28 days and a w cm of 0 40, presence of larger voids concrete treated in this way can.
usually only withstand a few centimeters of head pressure. Ramachandran 1995 For this reason stearates and other. hydrophobic materials are generally used only in conditions in. which there is little or no hydrostatic pressure, Polymer materials coalesce within the concrete mass to. form water repellent films Others have been reported to. form globules that plug capillaries once hydrostatic pressure. has been applied Some of these materials have been found. to resist hydrostatic pressure Ramachandran 1995 and can. be categorized as PRAHs Nevertheless concrete structures. containing these materials cannot be considered completely. watertight because polymers lack the ability to bridge cracks. formed by thermal or mechanical movement of the concrete. Kubal 2000 Leaking cracks are often addressed separately. using suitable repair methods The admixture supplier. should be consulted regarding the recommended method of. crack repair particularly for hydrophobic admixtures which Fig 15 2 Chloride penetration of a hydrophobic PRA. may repel water based repair materials One major use of subjected to ponding Tested using modified chloride ponding. polymer latex admixtures has been to reduce permeability of protocol not the AASHTO T259 procedure discussed in. Section 15 3 Cementitious content is 690 lb yd3 and w cm is. concrete overlays for bridge decks and parking decks. 0 40 Note 1 in 25 4 mm 1 lb yd3 0 5933 kg m3, Finely divided solids may reduce permeability under. nonhydrostatic conditions by increasing density or by simply. filling up voids leading to repellency The denser concrete crystalline deposits become integrally bound with the. has reduced porosity which restricts the movement of water hydrated cement paste The resulting concrete has signifi. however the pores are usually not completely blocked cantly increased resistance to water penetration under pres. These products are typically used for nonhydrostatic condi sure An overview of the general process may be represented. tions PRAN and in some cases are used in combination by the following. with hydrophobic chemicals for a synergistic effect 3CaO SiO2 MxRx H2O CaxSixOxR H2O x MxCaRx H2O x. SCMs such as fly ash raw or calcined natural pozzolans calcium silicate crystalline promoter water. silica fume ACI 232 1R 232 2R 234R or slag cement modified calcium silicate hydrate pore blocking precipitate. ACI 233R although not chemical admixtures can, contribute to reducing concrete permeability and can be a Similar reactions may exist involving the calcium. complementary component in a well proportioned mixture aluminates but the aforementioned process is expected to. incorporating permeability reducing admixtures Figures 15 3 predominate due to the abundance of calcium silicates. and 15 4 demonstrate the permeability under pressure of These crystalline deposits develop throughout the depth of. concrete mixtures containing fly ash and similar mixtures the concrete and become a permanent part of the concrete. containing a crystalline PRA at the age of 10 months The mass The crystalline deposits resist water penetration. crystalline admixture resulted in a significant reduction in against hydrostatic pressure and can be categorized as. permeability when added to the fly ash mixture PRAHs As hairline cracks form over the life of concrete. Unlike hydrophobic materials crystalline admixtures are crystalline admixtures continue to activate in the presence of. hydrophilic and the active ingredients react with water and moisture and seal additional gaps Kubal 2000 Skoglund. cement particles in the concrete to form calcium silicate and Johansson 2003 Cracks may still develop that exceed. hydrates and or pore blocking precipitates in the existing the self sealing property and admixture suppliers should be. microcracks and capillaries The mechanism is analogous to consulted regarding the recommended method of repair It. the formation of calcium silicate hydrates and the resulting has been reported that once fully cured crystalline systems. American Concrete Institute Copyrighted Material www concrete org. 48 REPORT ON CHEMICAL ADMIXTURES FOR CONCRETE ACI 212 3R 10. In addition to service conditions and level of performance. other factors will also contribute to the selection of a PRA. Some materials may affect the plastic properties of concrete. such as air entrainment setting time and water reduction. Also depending on the manufacturer PRAs are available in. either liquid or solid form and this will affect the method of. addition The basis for achieving low permeability concrete. and optimizing the performance of PRAs and other admixtures. is to address factors affecting the quality of the mixture. including proper proportioning and w cm quality of raw. materials and inclusion of supplementary cementing. materials and other admixtures Recommendations from. Fig 15 3 Permeability of concrete containing 20 Type F manufacturers of each PRA can guide the user with respect. fly ash and crystalline admixture,to the correct dosage rate and directions for use. The effects of the admixtures can be evaluated by testing. the permeability of concrete through both direct and indirect. methods The U S Army Corps of Engineers CRC C48 92. 1992 test method is a direct measurement of concrete. permeability resistance during exposure to water under 200 psi. 1 28 MPa of hydrostatic pressure After a steady state of. flow has been established Darcy s equation can be used to. calculate the coefficient of permeability K European. versions of this methodology such as DIN 1048 5 and BS. EN 12390 8 measure the penetration of water under hydro. static pressure into a concrete specimen The European. standards instruct the user to expose the concrete to 72 5 psi. Fig 15 4 Permeability of concrete containing 30 Type F 0 5 MPa of water for 72 hours The specimens are then split. fly ash and crystalline admixture in half and the depth of water penetration is measured A. widely used modification of the European standard is to. can withstand hydrostatic pressures of 400 ft 122 m of head expose the concrete to 150 psi 1 0 MPa for 96 hours and. Kubal 2000 then use Valenta s equation to calculate the coefficient of. permeability based on penetration depth Taywood Valenta. method The use of Valenta s equation requires the increase. 15 3 Selection and evaluation, in mass for each specimen to be accurately measured to.
ACI 233R although not chemical admixtures can contribute to reducing concrete permeability and can be a complementary component in a well proportioned mixture incorporating permeability reducing admixtures Figures 15 3 and 15 4 demonstrate the permeability under pressure of concrete mixtures containing fly ash and similar mixtures containing a crystalline PRA at the age of 10 months The

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