1、STDmACI SP-171-ENGL 2000 Obb2949 0551800 O19 I ERRATA SP-191 Water-Cement Ratio and Other Durability Parameters paper 3, page 27 Determination of Water-Cement Ratio in Hardened Concrete by Optical Fluorescence Microscopy, by U. H. Jakobsen, P. Laugesen, and N. Thaulow The synopsis as printed is inco
2、rrect. The correct synopsis is as follows: Synopsis: This paper describes a method for determining the water to cement ratio (WIC) of hardened concrete using optical fluorescence microscopy. The method is well established and has been used for many years. In Denmark the method is used for quality co
3、ntrol of hardened concrete. The method is based on vacuum impregnation of concrete using a yellow fluorescent epoxy. During impregnation the capillary porosity, cracks, voids, and defects in the concrete are filled with epoxy. The amount of fluorescent dye entering the cement paste depends on the ca
4、pillary porosity, which is determined 5y the wc and the degree of hydration. After impregnation and hardening of the epoxy a thin section of concrete with a thickness of 0.020 mm (20 p) is prepared. The thin section is analyzed under an optical microscope using a combination of a blue excitation fil
5、ter and a yellow blocking filter. This is the fluorescent light mode in which epoxy filling air voids and cracks appears yellow, cement paste as shades of green, and aggregate black. The shade of green of the cement paste depends on the capillary porosity. A sample with low WIC appears dark green, i
6、.e. has less fluorescence intensity dlie tc 2 107 maonnt efqoxy within the paste. A szrn?!e with high vdr appxu-s !i$-! gree1, Le. has high fluorescence intensity. These shades of green (fluorescence intensity) are used to determine the wc by comparing the fluorescence intensity of the cement paste
7、with standards of known wIc. This paper describes the fluorescent impregnation technique, the thin section preparation, the visual determination of wc and discusses the pitfalls in the WIC determination. Furthermore, the paper presents data from a quality assurance project and damage analysis and da
8、ta ofRound Robin Testing. STD.AC1 SP-LIL-ENGL 2000 W Obb2949 055LB02 991 W Water-Cement Ratio and Other Durability Parameters- Techniques for Determination Editor Mohammad S. Khan international SP-191 STD-AC1 SP-171-ENGL 2000 m 0bb2947 0551803 828 m DISCUSSION of individual papers in this symposium
9、may be submitted in accordance with general requirements of the AC1 Publication Policy to AC1 head- quarters at the address given below. Closing date for submission of discussion is September 1,2000. All discussion approved by the Technical Activities Commit- tee along with closing remarks by the au
10、thors will be published in the January/ February 2001 issue of either AC1 Structural Journal or AC1 Materials Journal depending on the subject emphasis of the individual paper. The Institute is not responsible for the statements or opinions expressed in its publications. Institute publications are n
11、ot able to, nor intended to, supplant indi- vidual training, responsibility, or judgment of the user, or the supplier, of the information presented. The papers in this volume have been reviewed under Institute publication proce- dures by individuals expert in the subject areas of the papers. Copyrig
12、ht O 2000 AMERICAN CONCRETE INSTITUTE P.O. Box 9094 Farmington Hills, Michigan 48333-9094 All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by any electronic or mechanical device, printed or written or or
13、al, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors. Printed in the United States of America Editorial production: Jane D. Carroll Library of Congress catalog card number:
14、 00-101382 PREFACE This volume contains eight of the 12 papers that were presented in a two-part session “Methods for Determining Water-Cement Ratio and Other Durability Parameters in Concrete,” sponsored by AC1 Committee 201, Durability of Concrete, at the 1998 Fail Convention in Los Angeles. I exp
15、ress my appreciation and thanks to Steve Forster and Gary Crawford, both of the Federal Highway Administration, who co-chaired the sessions with me. The authors who made presentations and contributed to this publication should be commended for coming forward and sharing their knowledge and experienc
16、e with their peers on many techniques that are not standardized yet and are still in the developmental stage. The efforts of the reviewers, many of them members of Committee 201, are equally commended for their constructive comments and suggestions that would contribute to refinement and maturity of
17、 several techniques included in this publication. On behalf of Committee 201, I thank all the authors and reviewers. This publication should be of interest to individuals involved in concrete failure investigations, particularly those related to durability, and in quality control efforts aimed at as
18、suring a durable structure. Academics, researchers, materials engineers, structural engineers, forensic engineers, and materials producers should ali benefit from the information presented in this publication. Editor Mohammad S. Khan iii CONTENTS CONCRETE DURABILITY-INFLUENCING FACTORS AND TESTING b
19、y S. W. Forster 1 COMPARISON OF KNOWN AND DETERMINED WATER-CEMENT RATIOS USING PETROGRAPHY by J. J. Liu and M. S. Khan ! . 1 1 DETERMINATION OF WATER-CEMENT RATIO IN HARDENED CONCRETE BY OPTICAL FLUORESCENCE MICROSCOPY by U. H. Jakobsen, P. Laugesen, and N. Thaulow . 27 PASTE MICROHARDNESS-PROMISING
20、 TECHNIQUE FOR ESTIMATING WATER-CEMENT RATIO by B. Erlin and R. A. Campbell . 43 RAPID ESTIMATION OF WATER-CEMENTITIOUS RATIO AND CHLORIDE ION DIFFUSIVITY IN HARDENED AND PLASTIC CONCRETE BY RESISTIVITY MEASUREMENT by K. A. MacDonald and D. O. Northwood . 57 LABORATORY AND FIELD EVALUATION OF NUCLEA
21、R GAGE FOR MEASUREMENT OF WATER AND CEMENT CONTENT OF FRESH CONCRETE by D. Whitting and M. Nag . 69 EVALUATION OF FOUR SHORT-TERM METHODS FOR DETERMINING CHLORIDE PENETRABILITY IN CONCRETE by K. Stanish, R. D. Hooton, and M. D. A. Thomas 81 PRACTICAL QUALITY CONTROL TEST PROGRAM FOR HIGH- PERFORMANC
22、E CONCRETE IN PRECAST CONCRETE TUNNEL LINERS by S. J. DeSouza, R. D. Hooton, and J. A. Bickley 99 Y STD-AC1 SP-LSL-ENGL 2000 Obb2949 0553806 537 SP 191-1 Concrete Durability-lnf luencing Factors and Testing by S. W. Forster SYNOPSIS Durability is defined in AC1 116R as the ability of concrete to res
23、ist weather- ing action, chemical attack, abrasion, and other conditions of service. Concrete can certainly be used to construct durable, long-lasting pavements and structures; we see numerous examples of this behavior daily as we go about our lives. Dura- bility remains an issue, however, because w
24、e also see some examples of concrete construction that have not been as distress-free, or lasted as long as we would have liked. In these latter instances, usually one or more aspects of the environ- ment, materials and mix design andor construction were not sufficiently consid- ered for the impact
25、they would have on the performance of the concrete used. The objective of this paper is to review the various aspects of concrete durability as considered by AC1 Committee 201, particularly as to the demands placed on the concrete as a material. Current methods used to explain the durability perfor-
26、 mance of in-service concrete or predict the performance of concrete to be placed will also be reviewed. The aspects of durability that affect and interact to produce the durability per- formance of concrete may be placed in five broad categories: freezing and thaw- ing; aggressive chemical attack;
27、surface abrasion; corrosion of embedded steel; and the alkali-aggregate reaction. Tests used to estimate concrete durability include microscopic examination, chemical techniques, characterization of the concrete components, and accelerated testing to simulate the durability aspect under consideratio
28、n. Interpretation of the performance of in-service concrete is made more diffi- cult by the fact that usually the deterioration is not caused by one type of distress, but involves a combination of factors. Kevwords: alkali-aggregate reaction; chemical attack; concrete durability; corrosion; freezing
29、 and thawing resistance 1 STD-AC1 SP-171-ENGL 2000 W 0662949 0553807 473 W 2 Forster Stephen W. Forster is a Research Geologist and Team Leader of the Portland Cement Concrete Pavement Team in the Office of Infrastructure Research and Development of the Federal Highway Administration (FHWA), Washing
30、ton, D.C. Dr. Forster is currently in charge of the research program on all aspects of concrete pavements, including the durability of the materials used. INTRODUCTION Durability is defined in AC1 116R (1) as the ability of concrete to resist weathering action, chemical attack, abrasion, and other c
31、onditions of service. Durability requirements according to the AC1 building code are found in AC1 3 1813 1 8R, Chapter four (2). The mission of AC1 Committee 201, Durability of Concrete, is “to develop and report information to ensure the production of durable concrete”(3). The factors that influenc
32、e durability, as addressed by AC1 201, will be considered herein. Concrete can certainly be a durable, long-lasting construction material; we see numerous examples of durable concrete in our daily lives. Durability remains an issue, however, because we also see some examples of concrete construction
33、 that have not been as distress-free, or lasted as long as they were designed to do. In these latter instances, usually one or more aspects ofthe environment, materials and mix design and/or the construction process were not sufficiently considered for the impact they would have on the performance o
34、f the concrete used. The objective of this paper is to review the various factors of concrete durability that may influence the long term performance of concrete in service, particularly as to the demands placed on the concrete as a material, and review the methods currently used to test and evaluat
35、e the durability performance of in-service concrete or predict the performance of concrete prior to placement. For the purposes of this paper, durability and deterioration will be limited to the following five main factors: freezing and thawing; aggressive chemical attack; surface abrasion; corrosio
36、n of embedded steel; and alkali-aggregate reaction. Concrete can range from very resistant to very susceptible to each of these deterioration mechanisms, depending on the characteristics of the concrete and the exposure conditions. In the following sections each of these factors of durability and th
37、e means of testing and evaluating them will be discussed. FACTORS INFLUENCING DURABILITY Freezing and Thawing The resistance of concrete to deterioration by freeze-thaw cycling can potentially involve two different components of the concrete: the cement paste and the aggregate. In order for freezing
38、 and thawing to have an effect on either component, however, they must be at some level of critical saturation at the time of freezing. In spite of extensive study and research on the subject, disagreement still exists STDmACI SP-171-ENGL 2000 9 Obb2949 0551408 30T Water-Cement Ratio and Other Durab
39、ility Parameters 3 as to the exact mechanism of stress development in the cement paste due to freezing while at a critical level of saturation. Early theories ascribed the damage to hydraulic pressures in the pores, generated by the resistance to water movement away from the area of freezing within
40、the paste. The magnitude of the pressure was thought to be related to the rate of freezing, with higher freezing rates generating greater pressures. The pressure was also believed to depend on the permeability of the paste and the distance necessary for the water to travel to reach a point of “escap
41、e” or pressure relief. Thus, the beneficial effect of entraining air in the concrete was explained as decreasing the distance necessary for the water to travel in order for an air void (site of pressure relief) to be encountered. Later theories relatedthe phenomenon to osmotic potential created as a
42、 result of increases in alkali concentrations in the unfrozen portion of the pore solution during freezing. This potential causes the water in the unfrozen pores to diffuse into the solution in the frozen pores. The dilution of water in the vicinity of ice allows additional ice formation (or ice acc
43、retion). This in turn can cause dilation pressure in the paste. In this scenario the entrained air voids serve as a preferred site for the unfrozen water, thus avoiding the distress due to the osmotic mechanism. The effect cf freezing and thawing on certain aggregates in concrete has to do with the
44、porosity, pore size distribution and permeability of the susceptible aggregates. The hydraulic pressure theory, described above for cement paste, may be the best explanation for the behavior of these aggregates. In general, it is the coarse aggregate fraction that causes the distress in concrete. Th
45、e susceptible aggregates typically have high porosity and absorption, with a majority of pores in the O. 1 to 5 Fm range. Pores in this size range can become saturated so that excessive pressures and cracking result during freezing. Large pores do not usually become completely filled with water, whe
46、reas any water in pores finer than the designated range usually does not freeze. Susceptible aggregates can lead to popouts near the surface of concrete. In concrete located in climates subject to freezing and thawing, these aggregates cause the phenomenon known as D-cracking. In this situation, the
47、 concrete near free edges and joints is exposed to sufficient water for the aggregate to become critically saturated. Upon freezing, expansion of the aggregate, and/or rapid expulsion of the water in the aggregate into the paste, cause disruptive pressures and cracking in the concrete parallel to jo
48、ints and free edges. Experience has shown that reduction in maximum aggregate size improves performance for the susceptible aggregates. Freeze-Thaw Durabiliy There are a number of recommendations for achieving concrete resistant to deterioration due to freezing and thawing. These include minimizing
49、the exposure to moisture; a low water-cementitious materials ratio; an adequate air void system; durable aggregates; adequate curing prior to exposure to the first freezing cycle; and good construction practices. Since the susceptibility of concrete to freeze-thaw deterioration depends on the degree of saturation, minimizing the exposure to moisture and moisture uptake will be very beneficial, where practical. Where lack of critical saturation is a sTD.ACI SP-LIL-ENGL 2000 Obb2949 0553809 24b 4 Forster certainty, additional specific steps to prevent damage due to freezing and thawin
