Emgimeer. Virginia. Highway and Transportation Research Council. opinions, findings, and conclusions expressed in this. Virginia

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1 Celik 0zyildirim H. Emgimeer Research opinions, findings, and conclusions expressed in this (The are those of the author and not necessarily those of report Highway and Transportation Research Council Virginia Cooperative Organization Sponsored Jointly by the Virginia (A of Highways & Transportation and Department University of Virginia) the FINAL REPORT NEOPRENE PADS FOR CAPPING CONCRETE CYLINDERS by the sponsoring agencies.) Charlottesville, Virginia March VHTRC 79-R39

2 238 CONCRETE RESEARCH ADVISORY COMMITTEE MR. J. E. GALLOWAY, JR., Chairman, Assistant Materials Engineer, VDI MR. T. R. BLACKBURN, District Materials Engineer, VDHST MR. B. W. BUTT, Assistant Construction Engineer, VDHST MR. C. L. CHAMBERS, Asst. Division Bridge Engineer, FHWA MR. JOHN W. CHILES, Resident Engineer, VDHgT MR. F. C. MCCORMICK, Professor of Civil Engineering, U. Va. MR. K. H. MURRAY, Professor of Civil Engineering, 01d Dominion Univ MR. W. R. MUSTAIN, Assistant District Engineer, VDHST MR. H. H. NEWLON, JR., Associate Head, VHgTRC MR. A. D. NEWMAN, District Materials Engineer, VDHgT MR. R. W. SCHWARTZ, District Bridge Engineer, VDHST MR. J. F. J. VOLGYI, JR., Bridge Design Engineer, VDH$T MR. R. P. WINGFIELD, Assistant Maintenance Engineer, VDHST ii

3 possibility of using neoprene pads as an alternate to The mortar for capping concrete specimens subjected to com- sulfur preliminary tests to determine the feasibility of the In two batches of concrete were prepared. Subse- investigation, in the main part of the investigation 8 batches of quently, were made. Concrete cylinders measuring 6 x 12 in. concrete fabricated at strength levels of about 3,000 psi and were psi in steel and cardboard molds. For each mold type, 5,000 were tested for compression using both the neoprene specimens and the sulfur mortar caps. The I/2 in. thick, 6 I/8 in. pads specimens tested with neoprene pads yielded slightly lower the strengths than did those tested with sulfur mortar compressive However, at the 95% confidence level the differences were caps. statistically significant. There also was no significant not between the results obtained with the specimens difference in steel molds and those prepared in cardboard molds. prepared SUMMARY pression tests was investigated. diameter neoprene pads had a 50-durometer hardness and were in in extrusion rings 6 1/2 in. in diameter. In general, placed The report includes recommendations for further tests. iii

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5 Celik Ozyildirim H. Engineer Research the testing of cylindrical concrete specimens for com- In strength, the importance of end conditions in securing pressive loading over the total bearing area is well recognized uniform emphasized in the literature. (I) In order to accomplish and loading, ASTM procedure C39-72 requires that the test uniform be capped if the ends are not plane within in. cylinders also requires that the ends should not depart from perpen- It to the axis by more than 0.5 degree. Nonuniform dicularity test results. Consequently, in testing laboratories variable concrete cylinders used for compressive strength tests hardened routinely capped in accordance with ASTM C using are of sulfur, high-strength gypsum, or calcium aluminate mortars In the Research Council laboratories sulfur mortar cement. used as the standard capping material because of its high is strength and convenience of use. However, the compressive of sulfur mortar on both ends of a specimen is application use of neoprene pads over the ends of the cylinders has been The in the literature as an alternative method for sulfur suggested caps in obtaining uniform loading. 2) Work at the New mortar State Department of Transportation (NYSDOT) (2) has shown York cylinders tested with neoprene pads exhibit average com- that strengths slightly higher (149 to 172 psi) than cylinders pressive sulfur mortar caps. That work has indicated that the magni- with of this difference is so small that no corrections need to tude made. Also, the testing variation for neoprene pads was found be be equal to or less than that of sulfur mortar caps. In the to FINAL REPORT NEOPRENE PADS FOR CAPPING CONCRETE CYLINDERS by INTRODUCTION caused by small irregularities in the surface lead.s loading erroneously low indications of compressive strengths and to and expensive. Its toxic fumes and the necessity time-consuming heating also constitute a safety and air pollution hazard. for

6 on the New York research the economic advantage, ease of report and safety benefits associated with neoprene pads are stated use, its use as an acceptable substitute for sulfur mortar caps and recommended. is prestressed concrete plant in Virginia aware of the research A the NYSDOT became interested in the use of neoprene pads. They at tests to verify the New York results a d informed the initiated Council of their i terest. It appears that the advantages Research accepted as successful. preliminary investigation of the feasibility of the study two a of concrete were used. These, coupled with the eight batches used in the main study, made ten batches yielding sixty batches x 12 in. specimens. Half of the. specimens were capped with 6 mortar and the remainder with neoprene pads. The specimens sulfur tested under compression and a statistical analysis was were to determine if significant differences existed between the made capping methods at the 95% confidence level. two as those used in the NYSDOT tests. The neoprene had a istics durometer hardness an.d the pads were 1/2 in. thick and 6 1/8 in. 50 diameter. The pads were located in extrusion rings 6 1/4 in. in diameter and placed on both ends of the cylinder. The use of in 6 1/4 in. durometer ring in lieu of the 6 1/2 in. ring used by the NYSDOT was adopted because of the experience reported by the the concrete plant in Virginia in its study of the NYSDOT procedure.(3) prestressed found that the wider 6 1/2 in. ring permitted They neoprene pads to stretch and flow outside the extrusion ring. the the smaller 6 1/4 in. ring was constructed for use Consequently, this study. Figure i shows a sketch and a picture of in neoprene a and extrusion ring. pad sulfur mortar used was a commercially available material The used by the Research Council. normally with the use of neoprene pads make it attractive and associated wide use of this capping method can be expected if it is generally a OBJECTIVE AND SCOPE objective of this study was to investigate the possible The of neoprene pads as an alternate to sulfur mortar caps. In use PROCEDURE _Mat e..r. i al. s Capping neoprene pads used were of the same size and character- The

7 i/4" I.D. (actual, 6 i/2" wall pipe, i/8" Dia. neoprene 6 i/2" thick pad, i Sketch and photo of neoprene pad Figure e.xtrusion ring. and

8 more extensive study in this area utilizing 6 i/ 4 in. extrusion a and the neoprene pads would be feasible and warranted. rings and Mix..Pr.opor.ti..on.s S.amp!es 6 x 12 in. cylinders were prepared from each of two Six Type I cement with fly ash. The air content of the former used 5% and that of the latter was 10%. was Batch No. were moist cured for 28 days. Half of the speci- Specimens were capped with sulfur mortar and the other half with mens compressive strength values of the specimens are The in Table 2. These results indicate that cylinders summarized with neoprene pads failed at slightly lower strengths broken those with sulfur mortar caps. For the first batch the than in average strength was 290 psi,.which is 5% of the difference obtained utilizing sulfur-mortar caps. The 190 psi strength for the second batch is also 5% of that attained by difference with sulfur mortar. The standard deviations for specimens te.sted with neoprene pads were smaller than those for cylinders cylinders with sulfur mortar caps. However, because of the the amount of data no significance can be attached to these limited results. Laboratory Study Preliminar preliminary lab study was performed to determine whether A of concrete. The mixture proportions of the two batches batches shown in Table i. Batch i utilized IP cement and Batch 2 are Table i Mix Proportions in Pounds Per Cubic Yard Cement Fly Ash Co A. F. A. Water.'.,,'..,,,., ,924 1, ,922 1,063 neoprene pads in extrusion rings. All were tested at 28 days. Results

9 Batch No. Compressive Strength Values 28-Day of 3 Specimens) (Average mort ar Deviation ]iii Illl view of the favorable results in the preliminary labo- In studies, a more extensive series of specimens were prepared ratory was desired to test cylinders at the lower and upper It levels expected to be attained in the field. The widely strength A3 concrete-has a 28-day minimum design strength of 3,000 used and the A5 concrete used in prestressed elements has psi a of 5,000 psi. Concretes prepared in the laboratory minimum the A3 or AS specifications would normally yield compressive using considerably higher than the minimum design strengths. strengths the specifications were not completely adhered to Therefore, an attempt was made to prepare specimens at about the 3,000 and and 5,000 psi levels. For each desired strength level 4 psi 3 were used in proportioning the mixtures. For the lb./yd. psi mixtures,. 588 lb. of cement per cubic yard was used 5,000 air entrainment was omitted to minimize variability. The and aggregate utilized in all the mixtures was a locally coarse granite gneiss with a specific gravity of 2.78 and a available rodded unit weight of lb./ft. 3 The fine.aggregate was dry quartz sand with a specific gravity of 2.62 and a fineness a of 2.8. The same Type II cement was used in all the modulus The mixture proportions for the low and high strength mixtures. are given in Table 3. concretes Table 2 Compressive Cap Strength Standard i 1, 5, i Neoprene pad Sulfur Ii0 mortar 5,520 3, Neoprene pad S u I fur 3, Ma in Te s t in g. Pro gr.am and tested. S amp i.e., s,.an d M., i x.. IP, Op,,O rt i, qns of concrete were prepared. For the 3,000 psi concretes, batches high air Content of about 10% and a cement content of 376 a

10 slump, air content, and unit weight f each batch are The in Table A-I of the Appendix. The average mixture data given low and high strength concretes and the corresponding for deviations are summarized in Table 4. standard Std. Average Std. Average Dev. Dev. lb. / ft. 3 Std. Dev. 6 x 12 in. cylinders were prepared from each of 8 batches Six concrete. Half of these cylinders were cast in steel molds of the other half in cardboard molds. For each mold type, half and the specimens, were tested under compression using sulfur of caps and the other half using the neoprene pads and mortar rings. extrusion Table 3 Mixture Proportions in Pounds Per Cubic Yard Strength Level Cement Water C.A. F.A ,869 1, ,869 1,416 High Table 4 Mixture Data (Average of 4 Batches) Slump, in. Air Content, % Unit Weight, Strength Level Average IIiiiI Low i High I li Results compressive strength test results for all the specimens The shown in Table A-2 of the Appendix. A three-level analysis are

11 variance test was performed using the data in Table A-2 to of if any significant differences existed among compressive determine same proportions for each strength level and were not assumed the be variables. The results indicated that, as expected, at to 95% confidence level there was a significant difference the the two strength levels. However, there were no signif- between differences between the specimens prepared i cardboard icant steel molds and tested with either neoprene or sulfur mortar and a statistical test was done to determine whether the Also in compressive strengths were different for cylinders variabilities with neoprene pads and sulfur mortar for each strength level. capped cast in both types of mold were included. The average Cylinders strength values and the standard deviations are compressive in Table 5. The results from the F test indicated summarized at the 95% confidence level variations in the compressive that for the two capping-methods were not significant. strengths Std. Dev. Std. Dev. specimens tested with neoprene pads tended to exhibit The splitting type of failure rather than the widely observed a type of failure of specimens with sulfur mortar caps conical illustrated in Figure 3. However, certain breaks were ob- as based on the three variables, namely, the mold type, strengths type, and strength level. The batches were prepared using capping caps. Table 5 Compressive Strength Values and Standard Deviations Average the Two Capping Types for Neoprene Pad Sulfur Mortar Level Strength Average, psi psi Average,,,,,rr,,, Low ,030 3, High 5,170 5,270 served to be similar in both capping methods.

12 3. Photographs of failed specimens Figure with neoprene pads. tested

13 of the high strength cylinders tested with neoprene pads So e explosively, but none of the sulfur mortar capped speci- ruptured general, the specimens tested using the neoprene pads In 50 durometer hardness in 6 1/4 in. extrusion rings gave aver- of on the limited number of tests performed in this study, based strength levels of 3,000 psi and 5,000 psi the differences at were not statistically significant at the 95% confidence noted There also was no significant difference between the level. obtained with specimens prepared in steel molds and those results in cardboard molds. prepared tested with neoprene pads tended to exhibit a Cylinders type failure, whereas those capped with sulfur mortar splitting more of a conical failure mode. However, some speci- displayed exhibited similar breaks with both capping methods. mens is recommended that, for a period of one year, from It field and laboratory projects specimens be fabricated selected testing with both capping methods. Ultimately, if differences for to be not significant, testing with neoprene caps should continue the laboratory it would be desirable to investigate the In of varying the diameter of the extrusion ring and the effect of the neoprene pad on the compressive strength of hardness cylinders. should be taken in testing high strength cylinders Precautions neoprene pads because of a possible explosive type rupture. with showed the same intense failure at the levels of strength mens At present, there is no explanation for this differ- encountered. It is noted that in other work at much higher strengths the ence. mortar caps were also found to rupture explosively. sulfur CONCLUSIONS compressive strengths slightly lower than similar specimens age the same batches) tested with sulfur mortar caps. However, (from RECOMMENDATIONS be an acceptable standard method of capping in the Department.

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15 appreciation is expressed to Tom Ellis, Chief Sincere Bayshore Concrete Products Corporation, Cape Charles, Engineer, thanks go to Stephen Runkle for his generous Special in the statistical phase of the study. Thanks are assistance to Clyde Giannini and Mike Burton for their invaluable given in the preparation and testing of specimens. help 2397 ACKNOWLEDGEMENT for the information on their experience with the Virginia, pads and extrusion rings. neoprene Ii

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17 F., "Effect of End Condition of Cylinder on H. of Concrete", Proceedings, American Strength J. S., and D. E. Amsler, "Capping Concrete Cylinders Grygiel, Neoprene Pads", Research Report 46, New York State with,- Department of Transportatxon, New York, communications with Tom Ellis, Chief Personal Concrete Products Corporation, Cape Bayshore 2399 REFERENCES ii Gonnerman, Compressive Society of Testing Materials, Vol. 24, Part 2, Engineer, e s, Charl Virginia. 13

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19 Batch No. High High I ump, S in. Level eoprene Sulfur $o. '.. ".i.... Sulfur,". L..,::.',,' Table A-I Mixture Data of the Batches Used in The Main Testing Program Unit Air, % Weig.h3t, Level lb. / ft. Strength Low 11.4 i Low Low Low High High Table A-2 Strength Test Data in PSI for Specimens Using Neoprene Compressive Sulfur Mortar Caps in Cardboard and Steel Molds and Hold Steel Mold Cardboard Batch Strength eoorene i Low 2,785,..',811 2,856 Low 3,112 3,139 3,201 3,165 3,236 3,068 2, ,130 3, 30 3,112 3,238 Low 3,006 3,077 2,997 3,395 3,077 3,185 High 5,367 5,131 5,287 5,199 5,119 5,570 5,358 5,0u.. 9 5,164 High 4,881 5,314 High 5,16. 5,199 5,.. 5,296 5,:4.38 S,199 5,23u. High 5,287 5,2 7 5,349

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