STUDY OF SHEAR STRENGTH PERFORMANCE ON ...Keywords : Glass, carbon, basalt Fiber reinforced polymer strips, UTM, ultrasonic pulse velocity test, epoxy resin, shear carrying capacity

STUDY OF SHEAR STRENGTHPERFORMANCE ON REINFORCEDCONCRETE BEAM WITH STRIPING

OF FRP STRIPS

Ashok Miriyala1, K.N. Lakshmaih2,1M.Tech Student, Civil Engineering

Narasaraopeta Engineering College (autonomous)Narasaraopet, Guntur

[email protected],Assistant Professor,

Civil EngineeringNarasaraopeta Engineering College (autonomous)

Narasaraopeta, [email protected]

June 22, 2018

Abstract

In Present scenario in the world, many structuresexisting the failures shear in the reinforced concretestructures and it is one of the critical problem inCivilStructures. As Shear failure is brittle in nature andidentified as the most disastrous failure mode, moreattention is required.The insufficient Shear strength mayoccur due to reason of different types of factors which arerelated to decreases in shear reinforcement or reduction inarea of steel due to effect in corrosion, sometimes theyneed to give more service load and having someconstruction errors etc. Hence, there need to increaseshear resistance of previous Reinforced Concrete structures

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International Journal of Pure and Applied MathematicsVolume 120 No. 6 2018, 4259-4281ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

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to meet current needs for present scenario in the world. Atpresent, the Fiber reinforced polymer (FRP) compositesare widely used for strengthening where as sticking of FRPstrips with epoxy resin is easy and effective instrengthening of structures. Beams, Slabs and Columnscan be easily repaired/rehabilitated with FRP stripsputting minimum effort. In this Present work,the beamsare strengthened in shear using FRP strips. The Beams ofsize is150mm x 200mm x 700mm and which were castedand cured for 28 days. In. Then FRP two layered strips ofGlass, Carbon and Basalt were stacked to beams by epoxyresin in two ways (1).FRP Strips of 67mm width,perpendicular to longitudinal axis of beam at a specifiedspacing and are designated as BGS-67, BCS-67, and BBS -67. (2). FRP Strips of 34mm width, perpendicular &inclined at 60.460to the longitudinal axis of beam and aredesignated as BGI-34, BCI-34, BBIS -34.Here ’G’ standsfor Glass, ’C’ stands for Carbon, and ’B’ stands for BasaltFRP strips. All the beams are examined under four pointbending on UTM about 100 tons capacity to know theshear carrying capacity and for all the beams are testedunder the ultrasonic pulse velocity test to know thestrength and quality of concrete.

Keywords: Glass, carbon, basalt Fiber reinforcedpolymer strips, UTM, ultrasonic pulse velocity test, epoxyresin, shear carrying capacity.

1 Introduction

Earlier structures have been constructed with significant numberof facilities using pre-stressed concrete and reinforced concretematerials. During next century several of them have entered theend of their planned service life. Many natural disasters especiallyearthquakes made necessary to increase the safety levels ofbuildings etc. That leads to consequences like steel corrosion,concrete cracking and spalling is observed frequently.

Several types of the structures were built to carry loads aresignificantly smaller than the current needs. Older structures thatwere designed using past codes are unsafe need to be upgraded.Entire re-installment of such deficit structures leads to increasing

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in extremely large amount of public money and time.Reconstruct/modification has become important for develop toincrease their load bearing capacity and stretching their servicelives. Hence it is a challenge for structural engineer to evaluateand implement effective and economical repair and strengtheningprograms. As infrastructure becoming aged worldwide has seizedthe interest of many researchers and organizations to find differentmaterials and methods to restore deteriorating and deficientstructures. Composites which are ahead in position have receivedgreat concentration as materials for choice for a variety ofapplications in repair and strengthening projects. The area ofcomposites in construction, and in particular for strengthening,has been one of the fastest growing new areas within civilengineering during the last 10 years. Much focus and effort hasbeen placed on understanding the behavior of Fiber ReinforcedPolymers (FRP) strengthened concrete structures.Shear failure iscatastrophic and occurs usually without earlier warning; thus it isdesirable that the beam fails in flexure rather than in shear. Manyexisting reinforced concrete (RC) members are found to beimperfect in shear strength and need to be repaired. Shearstrengthening is required when an RC beam is found imperfect inshear, or when its shear capacity falls below its flexural capacityafter flexural strengthening. A recent technique for the shearstrengthening of RC beams is to provide extra FRP webreinforcement, commonly in the form of bonded external FRPstrips/sheets. Over the past few decades, a large amount ofresearch has been conducted on this new strengthening technique,which has established its effectiveness and has led to a goodunderstanding of the behavior and strength of suchshear-strengthened beams. To fulfil these goals, RC beams whichfail in shear are casted and strengthened with different FRPconfigurations.

2 MATERIALS

2.1 cement

53 grade of ordinary Portland cement of (KCP CEMENT) withcode of IS 12269:1987 and it is used in this study.

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2.2 Fine Agrregate

Locally available natural river sand with specific gravity 2.63 isused, confirming to IS 383: 1970.

2.3 Steel bars (reinforcement)

The usage of longitudinal reinforcements are more wihich were high-yield strength deformed bars of 12mm and 8mm diameter. Four12mm diameter bars on top and two 8mm diameter bars on bottomside. The lateral ties were made from mild steel bars with 6mmdiameter. The yield strength of steel reinforcement used in thisexperimental program was determined by performing the slanderedtensile test on the bars.

2.4 Glass Fiber polymer

Glass Fiber Reinforced Polymers are a proven and successfulalternative that have numerous advantages over traditionalreinforcement methods, giving structures a longer service life. TheGFRP rebar is a structural ribbed reinforcing bar made of highstrength and corrosion Resistant glass fibers that are impregnatedand bound by an extremely durable polymeric epoxy resin. Thiscombination equals an engineered material system resulting inunique attributes that replace and supersede typical materialssuch as galvanized, epoxy coated and stainless steel Rebar. Forthe present study Glass Fiber Polymer is purchased from onlinestore. Properties of Glass Fiber Polymer are:

2.5 Carbon Polymer Fiber

Carbon fibre reinforced polymer (CFRP) is an extremely strongand light fibre-reinforced plastic which contains carbon fibres.Carbon fibers are mostly used for repair purposes of old structuralelement against shear and flexure; the material known as CFRP.However, in early 1990’s, researchers showed that carbon fiberscan be used inside the concrete instead of steel reinforcementshowing a significant improvement in flexural and tensile strengthof concrete. It is more durable, corrosion free and 5 times higher

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Figure 1: Glass Fiber Polymer

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tensile strength than steel and it has capacity of higher toleranceand mostly it is lighter

Figure 2: Carbon Fibre Polymer

2.6 Basalt Fiber Polymer

Basalt Fiber is a material made from extremely fine fibers ofbasalt, which is composed of the minerals plagioclase, pyroxene,and olivine. It has thermal resistance, chemical resistance andhaving mechanical strength. It is also an ecological friendliness.Basalt fibers shows 15-20 percentage of higher tensile strength andmodulus. Basalt is a natural material that is found in volcanicrocks. It is mainly used (as crushed rock) in construction,industrial and high way engineering. One can also melt basalt(1300-1700◦C) and spin it into fine fibers. When used as(continuous) fibers, basalt can reinforce a new range of (plastic

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and concrete matrix) composites. It can also be used incombination with other reinforcements (e.g. basalt/carbon).

Figure 3: Basalt Fibre Polymer

2.7 Epoxy Resin

Epoxy resin sealers form a high-build protective film on the concretesurface, producing a hard, long-wearing, abrasion-resistant finish.They also offer excellent water repellence. They are available clearor pigmented, if you wish to add color. Most products impart aglossy finish. Epoxy resin is much harder than acrylics. Water-based epoxies bond well to concrete and provide a clear finish, butthey are nonporous and do not allow trapped moisture to escape.Epoxies are probably the best choice for concrete countertops andfood preparation areas. Epoxy resins are relatively low molecularweight pre-polymers capable of being processed under variety ofconditions.

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Figure 4: Epoxy Resin

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3 METHEDOLOGY

Concrete mix of M30 grade is adopted from the past researchers.The concrete was casted by wrapping FRP strips of glass, carbon,basalt types. (1). FRP Strips of 67mm width, perpendicular tolongitudinal axis of beam at a specified spacing and are designatedas BGS-67, BCS-67, and BBS - 67. (2). FRP Strips of 34mmwidth, perpendicular & inclined at 60.460to the longitudinal axisof beam and are designated as BGI-34, BCI-34, BBIS -34.Here ’G’stands for Glass, ’C’ stands for Carbon, and ’B’ stands for BasaltFRP strips Strength properties are studied through. Beams of size150mm×200mm×700mm were prepared. Steel reinforcement cageconsists of 4#12mm on tension side and 2#8 mm on compressionside as longitudinal reinforcement and 6mm at 91.31 mm spacing asstirrups. Steel used is of Fe 415 grade. Reinforced concrete beamsare tested under two point loading on Universal testing machine(UTM) to find out modulus of rupture and shear carrying capacityand also tested under ultrasonic pulse velocity to know strengthand the quality of concrete.

4 EXPERIMENTAL

INVESTIGATION

A. TEST SPECIMENS

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Test specimens used for the present investigation are beams.The concrete beams of size 150mm200mm700mm were used astest samples to determine the shear carrying capacity. Thesamples were cast for M30 grade of concrete with coarse aggregateof size 20mm and 10mm. The feasibility of fresh concrete wasmeasured in terms of slump values. The ingredients of concretewere thoroughly mixed till uniform consistency was achieved. Forultrasonic pulse velocity test, same Beams of size150mm×200mm×700mm are used as test samples. These entirespecimens are casted by using different types of Fibres and testedon respective testing dates. Shear carrying capacity of reinforcedconcrete specimens is calculated by using Universal testingmachine (UTM).

Figure 5: Testing of conventional beam

B. MIX PROPORTIONSSamples are prepared for M30 grade concrete. For the design

mix IS: 10262-2009 recommendations are adopted. Mixproportions obtained are 1:1.59:2.12:1.45 with w/c ratio 0.45.

C. MIXINGThe individual mix ingredients are weighed with their

proportions exactly and then the materials are placed on a pan.The materials are thoroughly mixed in their dry conditions beforewater is added. The prepared mix was then immediately used fortesting fresh mix for workability. In this study, the early ageproperties of fresh concrete and mechanical performance andtensile strength of hardened concrete were examined. All tests

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were conducted using the following sample groups:1. Conventional concrete.2. Conventional concrete wrapped with Glass, Basalt, Carbonstrips of 67 mm and 34 mm width respectively.

D. CASTING OF SPECIMENSAfter applying oil to the moulds, as per the design mix

concrete was prepared. Casting of concrete specimens for thepresent investigation should be done for Beam moulds ofrespective sizes. These specimens are casted and tested as per IS516 1959 specifications.

Figure 6: Cages Prepared and Casting

E. CURING OF TEST SAMPLESAfter casting, specimens are immediately submerged in clean,

fresh water tank for curing of conventional concrete mix. Thebeams which were taken out of water were kept idle one day fordrying. The surface of the columns was smoothened by using sand

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paper to remove dust and surface roughness on the beams. Butfor the present investigation we are using epoxy resin as bondingagent. Before wrapping of FRP Sheet, epoxy resin base andhardener are mixed. By mixing epoxy resin it will comes in Lightgreen color. Mixing of chemical is must be done properly that itmixes thoroughly.By using a brush epoxy was applied on surfaceof beams and FRP sheet was stacked and wrapped around thebeams that they are kept undisturbed for 3 days for completehardening of epoxy.

Figure 7: Beams Wrapped With FRP Strips and Testing

F. FLEXURAL STRENGTH AND QUALITY OFCONCRETE

Flexural strength or modulus of rupture for the samples ofbeam specimens are tested on Universal testing machine (UTM)at 28 days for all the different beams ultra-sonic pulse velocitytest is done.

5 RESULTS AND DISCUSSIONS

The above table shows that, the maximum load obtained for thebeam of BCS-67 (Beam Carbon straight strip of 67mm widthdouble layered) is 445.7 KN and the load obtained forconventional beam is 172 KN which is very less. The percentageincrease in BCS-67 is 159.12% as compared to conventional beam.

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Figure 8: Ultrasonic Pulse Velocity Testing Of Beams

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And the next level of percentage increase in beam is BCI 34 & ithas better load of 402.35kN. So the beams of the carbon stripshaving maximum load carrying capacity. Therefore the BCI 34and BCS 67 beams resists the maximum tensile strength ascompared to the conventional beam. The main advantage of thiscarbon fiber is having more tensile strength as compared to theother FRP Strips

Figure 9: Increased Percentages in Load

From the above bar chart, the beam of BCS-67 increased133.92% as compared to conventional beam and also carriedmaximum load of 445.7 KN as compared to all other types ofbeams. From table the maximum displacement is observed for thebeam of BCS-67 is 13.7mm due more load carrying capacity.

A. Load Vs Displacement CurvesFrom the Fig the Load vs Displacement curve for BCS-67 has

been drawn. In BCS-67, carbon fiber of two layers were wrappedto strengthen the beams. The midpoint deviations were correlatedwith the conventional beam and shown in Fig 32 from where it

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Figure 10: Load Vs Displacement curve for BCS-67

can be finished that the deviated value is decreasing bystrengthening the beams and by increasing the layers of BCS, thestiffness of beam increases marginally In this curve it has beenobserved that load moved up to 445,700 N from there point ofbreakage is found and curve automatically comes down due todecrease in load bearing capacity simultaneously displacement atmaximum load is at 13.7 mm and comes up to 15.9 mm until totalbreakage of beam. From the below Fig shows that among allbeams BCS-67 has high percentage increase in load which isabout 159.12 and the second percentage increase in load is forbeam designated BCI-34 which is about 133.92 and leastpercentage increase in load is for beam designated BGI-34 whichis about 73.72.

B. Velocity of Ultrasonic PulsesIn this test, the strength and quality of concrete or rock is

assessed by measuring the velocity of an ultrasonic pulse passingthrough a concrete structure or natural rock formation. This test

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is conducted by passing a pulse of ultrasonic wave throughconcrete to be tested and measuring the time taken by pulse toget through the structure. Higher velocities indicate good qualityand continuity of the material, while slower velocities mayindicate concrete with many cracks or voids.Quality of concrete interms of strength, homogeneity, trapped air, internal flaws, cracks,segregation, honeycombing, compaction, workmanship, anddurability can be concluded from this test. The test can also beused to evaluate the effectiveness of crack repair.The ultrasonicpulse is generated by an electro acoustical transducer. When thepulse is induced into the concrete from a transducer, it undergoesmultiple reflections at the boundaries of the different materialphases within the concrete. A complex system of stress waves isdeveloped which includes longitudinal (compressional), shear(transverse) and surface (Rayleigh) waves. The receivingtransducer detects the onset of the longitudinal waves, which isthe fastest. Because the velocity of the pulses is almostindependent of the geometry of the material through which theypass and depends only on its elastic properties, pulse velocitymethod is a convenient technique for investigating structuralconcrete. The underlying principle of assessing the quality ofconcrete is that comparatively higher velocities are obtained whenthe quality of concrete in terms of density, homogeneity anduniformity is good. In case of poorer quality, lower velocities areobtained. If there is a crack, void or flaw inside the concrete whichcomes in the way of transmission of the pulses, the pulse strengthis attenuated and it passes around the discontinuity, therebymaking the path length longer. Consequently, lower velocities areobtained. The actual pulse velocity obtained depends primarilyupon the materials and mix proportions of concrete. Density andmodulus of elasticity of aggregate also significantly affect thepulse velocity. The table below shows the time of travel andvelocity of ultrasonic pulses in BCS-67 the ultrasonic pulsespassing through the concrete beam and velocity of pulses arenoted. Thus the maximum UPV (sec) observed at load of 400 KNat 398 sec and maximum velocity is observed at loads of 30 and 60KN at 5076 m/sec. Minimum UPV is observed at loads of 30 and60 at 137.9 sec and minimum velocity is observed at loads of 350and 400 KN at 2292 and 1757 respectively.

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For all the beams were tested by ultrasonic pulse velocity testand noted time of travel of waves and velocity till the beam getsdamaged. Fig shows variation of velocity for all beams vs loads.

From fig below variation of velocity for all beams vs loads themidpoint deviated values of all the beams strengthened werecorrelated with the conventional beam individually and it wasfound that, by strengthening the beams wrapped with carbonfiber strips shows, the stiffness increased and deflection valuesreduced fairly.

6 SCOPE FOR FURTHER WORK

It gives a great scope for further studies. Following areas are takesfor further research work in future:

• Exploratory study of reinforced concrete beams with orwithout opening

• Analysis of RC beam in case of Non-linear study

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Figure 11: Variation of Velocity for All Beams Vs Load

• Investigation of the bond mechanism between CFRP, GFRPand BFRP and concrete substrate.

• FRP strengthening of RC T-beams with different types offibres such as carbon, glass & basalt.

• Build-up of Reinforce Concrete L-beams with FRP composite.

• Build-up of Reinforced Concrete L-section beams with webopening.

• Effects of web openings of different shape and size on theshear behaviour of beams.

• Effects of shear span to depth ratio on shear strengthening ofbeams.

• Numerical modelling of RC beams strengthened with FRPsheets anchored at the end.

7 RECOMMENDATIONS

• The use of this glass, carbon, basalt, fibers can be encouragedin various applications in conventional concrete as well as inmany types of concrete in civil infrastructure.

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• Carbon, glass, basalt are here fine which leads to increase inload carrying capacity.

• In this project all the three fibers are used as strips not asfull sheets for cost effectiveness.

• The effect of fibers and physical properties canalsobe studied.

• Using fibers in conventional concrete increases the strengthcapacity and life span of structure.

• Using of Epoxy resin it is more resistant to hightemperatures, high flexible design, excellent aestheticappearance, High levels of dimensional stability.

8 CONCLUSION

Following are the conclusions from the study:

1. As Compared with conventional beam (CB), all FRPstrengthened beams are showing increased shear carryingcapacity.

2. As Compared to the conventional beam (CB), the percentageincrease in the load bearing (shear strength) capacity of BGS-67 is 84.36%, BGI-34 is 73.72%, BCS-67 is 159.12%, BCI-34is 133.92%, BBS-67 is 74.24%, and BBSI-34 is 80.34%.

3. The increased Percentage of load carrying capacity ismaximum for BCS-67 which is having 159.12% (maximumload is 445.7KN) of c conventional beam out of allstrengthened beams.

4. Straight strips are more effective in carrying more load whencompared to both inclined & straight strips.

5. For BCS-67 displacement at maximum load is 13.7mm whichis maximum when it is compared to all other beams due tohigh load carrying capacity.

6. Beams with straight strips are more ductile, as thedisplacement is more, when it is compared to beams withboth inclined and straight strips.

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7. By observing ultrasonic pulse velocity variation, the velocitydrop is less in case of BGI-34, BGS-67 and BCI-34.

8. Beams with Glass FRP strips have better crack arrestingproperty as they have less velocity drop due.

9. Out of all three types of FRP used CARBON is giving betterresults. Shear strengthening of beams with FRP strips iseffective and easy though having some drawbacks against fireand weathering. The original strength/capacity of beam inshear can be improved

Acknowledgment

I take this opportunity to convey our gratitude to all those who havebeen kind enough to offer their advice and provide assistance whenneeded which has led to the successful completion of the project.

I extend my sincere thanks to our guide Mr.K.N.LAKSHMAIAH,M.E, Assistant professor, Department ofCivil Engineering for his consistent guidance and support. Hispersisting encouragement, everlasting patience and keen interestin discussion have benefited us to the extent that cannot bespanned by words.

We are greatly indebted to the head of department of CivilEngineering NARASARAOPETA ENGINEERING COLLEGE(Autonomous)Mr. S.KANAKAMBARAO, M.E, (Ph.D.) forproviding support and stimulating environment in which theproject has been carried out. We are profoundly grateful towardsthe unmatched services rendered by him

We are thankful to our principal Dr. M. SRINIVAS KUMARforproviding us necessary infra-structure

I also thank all the teaching and non-teaching members ofdepartment of civil engineering with whose timely help thecompletion of our project work was possible.

References

[1] Aman Dangi1, Abhishek Arya2.Strengthening of ShearDeficient RCL and .T- Beams with Externally Bonded FRP

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[2] T. H. Patel1, Dr. K. B. Parikh2 .Strengthening of ReinforcedConcrete Beams with Fiber Reinforced Polymer Sheets withDifferent Configurations in Shear and Flexure: A CriticalReview .IJETA (ISSN 2250-2459, ISO 9001:2008 CertifiedJournal, Volume 6, Issue 1, January 2016)

[3] Sandeep G. Sawant, A. B. Sawant, M. B. Kumthekar.Strengthening of RCC beam- using different glass fiber. IJIES,ISSN: 23199598, Volume-1, Issue-2, January 2013.

[4] J.F. Chena and J.G. Tengb.Shear capacity of FRP-strengthened RC beams: FRP deboning. Construction andbuilding materials February 2003.

[5] I. A. Bukhari*, R. L. Vollum, S. Ahmad* and J. Sagaseta.Shearstrengthening of reinforced concrete beams with CFRP.Magazine of Concrete Research, 2010, 62, No. 1, January, 6577

[6] Khalifa, A., Tumialan, G., Nanni, A. and Belarbi, A., ”ShearStrengthening of Continuous RC Beams Using ExternallyBonded CFRP Sheets,” SP-188, American Concrete Institute,Proc., 4th International Symposium on FRP for Reinforcementof Concrete Structures (FRPRCS4), Baltimore, MD, Nov.1999, pp. 995-1008.

[7] Bjorn Taljsten*. Strengthening concrete beams for shear withCFRP sheets. Construction and Building Materials 17 (2003)1526

[8] Taljsten B. Strengthening of beams by plate bonding. J MaterCivil Eng 1997; 9(4):206 12.

[9] Chen JF, Teng JG. A shear strength model for FRP-strengthened RC beams. International Conference FRPRCS-5, vol. 1, University of Cambridge, ISBN: 0 7277 3029 0, July2001:20514.

[10] M. C. SUNDARRAJA* AND S. RAJAMOHAN, DIVYABHASKAR. Shear Strengthening of RC Beams Using GFRP

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[11] Zhishen Wu1, Xin Wang1 and Gang Wu2. basalt FRPcomposite as reinforcements in infrastructure

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STUDY OF SHEAR STRENGTH PERFORMANCE ON ...Keywords : Glass, carbon, basalt Fiber reinforced polymer strips, UTM, ultrasonic pulse velocity test, epoxy resin, shear carrying capacity