FLEXURAL STRENGTH – A MEASURE TO CONTROL …

1 International Journal of Scientific & Engineering Research, Volume 5, Issue 11, November-2014 46. ISSN 2229-5518. FLEXURAL STRENGTH A MEASURE to CONTROL Quality of Rigid concrete Pavements Jayant Damodar Supe* & Dr. **. *Associate Professor , Dept of Civil Engg. SSIET , Durg. **Professor & Head Dept. of Civil Engg. BIT , Durg . Abstract- FLEXURAL STRENGTH is a MEASURE of the tensile STRENGTH of an unreinforced concrete beam or slab to resist failure in bending. It is useful in knowing the quality of concrete work done in road construction. Because of low initial cost, flexible roads are preferred, to concrete road pavement, but bituminous roads gets deteriorated during rainy season and maintenance becomes costly, therefore Government agencies have decided to go for concrete roads.

2 Generally limestone as coarse aggregates for concrete roads are preferred but sometimes may not be easily available at all places nearby, therefore its replacement is necessary. Impact test, abrasion test & water absorption test were performed on demolished building waste concrete also, to recommend its suitability in making concrete roads as per Indian Standards Importantly boiling water curing has been done on some samples before FLEXURAL STRENGTH test for determining early STRENGTH of concrete , for predicting later age STRENGTH of concrete in roads. Behavior of FLEXURAL STRENGTH of concrete roads with lime stone, locally available is studied in this paper for concrete pavements. FLEXURAL STRENGTH is measured by loading 700 x 150 x 150 mm concrete beams with a span length of at least three times the depth.

3 The FLEXURAL STRENGTH is expressed as Modulus of Rupture (MR) in psi (MPa) and is determined by standard test methods ASTM C 78 (third-point loading). FLEXURAL MR is about 10 to 20 percent of IJSER. compressive STRENGTH depending on the type, size and volume of coarse aggregate used. However, the best correlation for specific materials is obtained by laboratory tests for given materials and mix design. Keywords Impact test, abrasion test, Flexure test, demolished waste, concrete roads .. 1 INTRODUCTION. In New Delhi, recently elected Minister of In India over 626 million tones of construction transport & shipment Gadkari and demolition waste is produced every year, noticed that during rainy season the flexible which is 52 times more than the ministry of pavement roads gets deteriorated due to water environment and forests estimate of logging, (apparent from photographs construction and demolition waste.)

4 Thus huge attached). Therefore government has resolved quantity of demolished building waste is being that in future all National Highways should be generated by large infrastructure projects made with rigid pavements. Earlier during across the country with serious environment Congress government rule also Delhi Chief consequences. To make value added reuse of Minister Dixit favoring concrete concrete waste the authors carried out various roads over bitumen roads in capital, invited tests on demolished concrete waste for testing chamber members CII and ACC and other its suitability in concrete beams for concrete largest companies agreed to explore the road pavements decreasing the requirement to possibility of workable solution of conversion use virgin non-renewable resources so that of all flexible pavement roads into rigid fresh lime stone can be replaced by pavement.

5 In the seminar organized by CII demolished concrete waste. The results are along with department of Industrial policy and found encouraging as discussed in this report. promotion, Government of India favored concrete roads construction for its long lasting nature and low cost maintenance. IJSER 2014. International Journal of Scientific & Engineering Research, Volume 5, Issue 11, November-2014 47. ISSN 2229-5518. Photo 1 Water logging problems with Flexible Pavements Photo 2 Cracks in Rigid Pavement As discussed earlier flexible pavement are not Also it has been proved that driving on preferred now a days in road construction concrete roads offer significant fuel savings because it gets damaged in rainy season compared to other type of roads, which (Photo 1) due to heavy rain and also due to ultimately results in reduction in Co 2 emission heavy traffic it gets detoriated hence ,hence reduction in global warming.

6 The IJSER. continuous maintenance is required . Also reason for the lower fuel consumption is due there is expansion and contraction of bitumen to the concrete surfacing lower rolling in flexible pavement which also reduces its resistance value. This can be attributed to life. Construction cost of concrete pavement is differences associated with macro texture and high as compared to flexible pavement even pavement stiffness , though it is preferred due its low maintenance cost and long life . Load Distribution in case of Rigid & Flexible Pavements A rigid concrete pavement distributes heavy roadbed ( ). Therefore flexible pavements loads over a relatively wider area, with fail also due to impact load if proper minimal pressure on the sub-grade the settlement is not done also during rainy season natural soil under the roadway.

7 On the other if water seeps under the flexible pavement and hand, flexible asphalt material concentrates if soil is loose ,make the sub-grade soil weak weight and transmits it deeper into the resulting in overstress in upper flexible layer, hence resulting in its Widespread use of concrete roadways failure, where as concrete pavement acts as produces a significant positive economic bridge over the sub-grade, hence less stress on impact on the movement of goods due to sub-grade also less effect of water . construction of smoother and quieter concrete pavements in recent years. IJSER 2014. International Journal of Scientific & Engineering Research, Volume 5, Issue 11, November-2014 48. ISSN 2229-5518.

8 Also it has been seen concrete pavement concludes that the light colour of concrete reflects light in a diffuse manner, compared to results in a cost-saving of up to 31 percent for the slightly spectral (somewhat mirror-like) night-lighting, including construction, energy reflectiveness of asphalt pavement. As a consumption and maintenance, when result, a concrete highway requires fewer compared with the lighting requirements of lights per unit length of pavement to achieve asphalt pavement. the same level of illumination. The report 2 Theory of Flexure Test When an object formed of a single material, will be at its maximum tensile value. These like a wooden beam or a steel , is bent it inner and outer edges of the beam are known experiences a range of stresses across its depth as the 'extreme fibers'.

9 Most materials fail ( ). At the edge of the object on the inside under tensile stress before they fail under of the bend (concave face) the stress will be at compressive stress, so the maximum tensile its maximum compressive stress value. At the stress value that can be sustained before the outside of the bend (convex face) the stress beam or rod fails is its FLEXURAL STRENGTH . IJSER. Fig. 2 - Beam of material under Bending & Stress distribution across beam Why Flexure STRENGTH test is required? acceptance of pavements. Very few use FLEXURAL testing for structural concrete . Agencies not using Designers of pavements use a theory based on FLEXURAL STRENGTH for field CONTROL generally find the FLEXURAL STRENGTH .

10 Therefore, laboratory mix design use of compressive STRENGTH convenient and based on FLEXURAL STRENGTH tests may be required, or reliable to judge the quality of the concrete as a cementitious material content may be selected delivered from past experience to obtain the needed design MR. Some also use MR for field CONTROL and Fig. 3 Third point loading half the load is applied at each third of span length 3. Problems with Flexure STRENGTH ? IJSER 2014. International Journal of Scientific & Engineering Research, Volume 5, Issue 11, November-2014 49. ISSN 2229-5518. FLEXURAL tests are extremely sensitive to testing variations to be useable as a basis for the specimen preparation, handling, and curing acceptance or rejection of concrete in the field procedure.