20320130406013 2-3

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20320130406013 2-3

  1. 1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME TECHNOLOGY (IJCIET) IJCIET ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December, pp. 126-133 © IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2013): 5.3277 (Calculated by GISI) www.jifactor.com ©IAEME EFFECT OF RAPIDITE ON STRENGTH OF CONCRETE IN WARM CLIMATES Sameer ul Bashir1, 1 Younis Majid2, Ubair Muzzaffer Rather3 B.Tech, NIT, Hazratbal, Srinagar B.Tech, COET, BGSBU, Raouri 2, 3 ABSTRACT The Present work is a part of series of experiments to study the influence of rapidite on strength of concrete. Rapidite is an admixture, which is used in cold weather concreting especially in Kashmir, as of its availability, low costs and non-existence of other alternatives which could nullify the effects of low temperatures on strength of concrete. In Kashmir, the winter temperatures fall to sub zero level and thus, rapidite is used as it has been a determined Accelerator and anti freeze agent. The present work has, however, been carried out in warm climate, when temperature was around 20 degree Celsius, to check the influence and hence, its suitability regarding various properties of concrete, particularly the strength of concrete. A nominal mix of M20(1:1.5:3) was used. Various strength tests were carried out after 7 days and 28 days of curing. 50% of specimen were tested at 7 days and remaining 50% at 28 days age. Various tables and various Graphs were prepared to study the effect of Rapidite on various properties of concrete which are discussed in the following sections of this paper. Keywords: CONCRETE, RAPIDITE, STRENGTH. CONCRETE Concrete is a composite construction material, composed of cement (commonly Portland cement) and other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate made of gravel or crushed rocks such as limestone, or granite, plus a fine aggregate such as sand), water and chemical admixtures. Concrete is used to make pavements, pipe, architectural structures, foundations, motorways/roads, bridges/overpasses, parking structures, brick/block walls and footings for gates, fences and poles. Concrete is used more than any other man-made material in the world. As of 2006, about 7.5 cubic kilometers of concrete are made each year—more than one cubic meter for every person on Earth. 126
  2. 2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME Reinforced concrete, prestressed concrete and precast concrete are the most widely used types of concrete functional extensions in modern days. Concrete solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. The water reacts with the cement, which bonds the other components together, eventually creating a robust stone-like material. PORTLAND CEMENT + H2O + ROCK = HARDENED CONCRETE + ENERGY (HEAT) COLD WEATHER CONCRETING In India certain regions experience sub-zero temperatures in winter. Concrete structures in such regions undergo cycles of freezing and thawing and there durability is affected due to frost action. Fresh concrete contains considerable quantity of fresh water which gets converted into ice lenses at freezing temperature. The ice formation in fresh concrete results in about 9% rise in volume and causes permanent damage to concrete and structural integrity cannot be recovered even if the concrete is made to harden later at high temperature. Even during hardening the concrete should be protected from extremely low temperature hence while concreting in cold weather ensure that the temperature of fresh concrete is maintained above 0 °C and temperature during first six hrs of casting should not be less than 5 °C. IS 7861 part II defines Cold Weather Concreting as Any operation of concreting done at about 5°C atmospheric temperature or below. ACI 306 “Cold Weather Concreting” defines cold weather concreting as a period when for more than three (3) consecutive days, the following conditions exist: The average daily air temperature is less than 5°C (40°F) and, The air temperature is not greater than 10°C (50°F) for more than one-half of any 24 hour period. Considering the above criteria our work can definitely be not called as the cold weather concreting as the temperature was around 20 degree Celsius. • • ADMIXTURES Definition IS 9103 : 1999 defines admixture as “A material other than water, aggregates, and hydraulic cement and additives like pozzolana or slag and fibre reinforcement used as an ingredient of concrete or mortar and added to the batch immediately before or during its mixing to modify one or more of the properties of concrete in the plastic or hardened state.” Benefits of Admixtures Admixtures confer several beneficial effects on concrete including reduction in water requirements, increased workability, controlled setting, accelerated hardening, improved strength, better durability, desired coloration and volume changes. The major reasons for using admixtures are: 1. To achieve certain properties in concrete more effectively than by other means. 2. To maintain the quality of concrete during the stages of mixing, transporting, placing, and curing in adverse weather conditions. 3. To overcome certain emergencies during concreting operations. Despite these considerations, it should be borne in mind that no admixture of any type or amount can be considered a substitute for good concreting practice. 127
  3. 3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME RAPIDITE Rapidte is a commonly used admixture in Kashmir during winter to accelerate the strength gain of concrete. It falls under Type C on the basis of ASTM classification i.e., it acts as accelerator. It also acts as antifreeze, depressing the freezing point of water and hence protecting the fresh concrete. RAPIDITE 2 IN 1 is a specially developed Concrete Set Accelerator, a ready-to-use, liquid admixture. It accelerates initial setting time (cement-water chemical reaction HYDRATION) of normal mortar and concrete and acts as anti-freeze within cement concrete. It improves workability and strength while fastening the hydration of cement . It makes the mix easier to place and speeds construction by shortening the initial set and curing time. Time and labor are saved, because forms and other protection can be removed earlier, and finishing can be started. Uses RAPIDITE 2 in 1 is recommended for use during cool and cold weather to accelerate the set time and reduce the risk of frozen mortar and concrete mixes. Features/Benefits • Accelerates initial set time . • Increases compressive strength. • Provides Anti –freeze properties. • Speeds up hydration of cement. • Increases workability of concrete or mortar mix in colder temperatures. EXPERIMENTAL INVESTIGATION Objective The objective of this project was to study the effect of a commonly used admixture RAPIDITE in Kashmir on the strength of concrete. Casting was done during March and April. The Percentage of RAPIDITE was varied to find its effect on the strength. Two castings for every percentage of rapidite, one plain and one with admixture, and relative change in various strengths of concrete at various ages was found. Following tests were conducted on concrete to study the effects of rapidite on concrete. TESTS CONDUCTED ON FRESH CONCRETE Slump Test for Workability Only slump test was used to find the workability of fresh concrete in each casting separately for PCC and Rapidite castings. TESTS CONDUCTED ON HARDENED CONCRETE COMPRESSION TEST: This test is conducted on cubes (150mm) which are loaded on their opposite faces in a Compression Testing Machine (CTM).The load at which first crack appears is considered as failure load and the compressive strength is calculated corresponding to this particular value of load. Compressive strength = Load at failure /Cross sectional area Where, cross-sectional area = (150×150) mm2 128
  4. 4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME SPLIT TEST: The test is carried out by placing a cylindrical specimen, horizontally between the loading surfaces of a Compression Testing Machine and the load is applied until failure of the cylinder, along the vertical diameter. The loading condition produces a high compressive stress below the two surfaces to which the load is applied. But the larger portion corresponding to depth is subjected to a uniform tensile stress acting horizontally. It is estimated that the compressive stress is acting for both (1/6) th depth and the remaining (5/6) th depth is subjected to tension. The horizontal tensile stress is given by the following equation: Horizontal tensile stress=2p/πDL Where, P = Load at failure L = Length or height of cylinder (300mm) D = Diameter of cylinder (150mm) FLEXURAL TEST: Flexural strength test of concrete is performed on beams. The loading applied on the beam is a two point loading in which loads are applied at (1/3) rd points of the beam. The beam is placed in the testing machine in such a way that the load points are 16.6 cm apart from each other as well as from each support. The load is increased until the specimen fails and this load is noted as failure load. Flexural strength is then calculated from the following formula: Flexural strength =2pl/bd2 Where, P l b = (Load at failure)/2 = Length of beam between supports (500mm) = Breadth of beam (100mm) TEST RESULTS Rapidte percentage was changed as 0.8,1,1.2, 1.4 and 1.6 and mean temperature noted was 20 degree celcius. Casting Number TABLE 1 SLUMP TEST RESULTS Volume of Slump for Rapidite water PCC (cm) Percentage Slump for concrete with rapidite(cm) 1 0.4×15 kg=6 kg 15.5 0.8% 12.8 2 6 kg 14.5 1% 16 3 6 kg 13.5 1.2% 16.6 4 6 kg 16 1.4% 16.8 5 6 kg 15.3 1.6% 16.2 Note : w/c ratio used was =0.4 129
  5. 5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME Casting Number Table 2: 7 and 28 day Average Strength test Results Description Compressive Tensile strength(cube) in strength(cylinder) in Mpa Mpa Flexural strength(beam) in Mpa 7 day 5 28 day PCC 20.46 24.88 1.134 1.59 3.33 3.72 17.21 20.64 1.175 1.43 1.76 2.55 PCC 19.64 23.08 1.185 1.67 2.94 5.21 17.1 21 1.499 1.67 2.94 3.33 PCC 21.5 30.8 1.487 2.05 2.19 4.9 17.9 26.18 1.4 1.7 1.37 4.9 PCC 20.5 26.2 1.26 1.7 3.5 3.7 Concrete with 1.4% Rapidite 4 7 day Concrete with 1.2% Rapidite 3 28 day Concrete with 1% Rapidite 2 7 day Concrete with 0.8% Rapidite 1 28 day 18.21 23 1.29 1.58 2.1 3.33 PCC 20.5 26.2 1.26 1.7 3.72 3.9 1.56 3.33 0.981 Concrete with 17.49 21.9 0.88 1.6% Rapidite Note: Rapidite was taken as Percentage by weight of cement PCC means plain cement concrete. RESULTS AND DISCUSSIONS: In order to study the effects of using accelerating admixture Rapidite at varied dosages (as shown in Table 5.3) onvarious strengths at 7 days and 28 days respectively, a comparative study of the test results achieved at different Rapidite percentage is performed. Following Comparisons are studied by plotting the graphs: • • • • • • Variation of 7 day compressive strength with Rapidite % Variation of 28 day compressive strength with Rapidite % Variation of 7 day tensile strength with Rapidite % Variation of 28 day tensile strength with Rapidite % Variation of 7 day flexural strength with Rapidite % Variation of 28 day flexural strength with Rapidite % 130
  6. 6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME The following graphs represent the comparative study: 25 1.6 PCC 1.4 20 Rapidi te Tensile Strength In Mpa Compressive Strength in Mpa 1.2 15 PCC 10 Rapidite 1 0.8 0.6 0.4 5 0.2 0 0 0 0 0.5 1 1.5 0.5 1 1.5 2 2 Rapidite % Rapidite % G1: Variation of 7 day compressive strength with Rapidite % G2: Variation of 7 day tensile strength with Rapidite % 35 3.5 30 Flexural Strength in Mpa 4 PCC Rapi dite 3 25 Strength (Mpa) 2.5 20 2 15 1.5 1 10 0.5 5 0 0 PC C 0.5 1 1.5 0 2 0 Rapidite % G3: Variation of 7 day flexural strength with Rapidite % 0.5 1 1.5 Rapidite %age 2 G4: Variation of 28 day compressive strength with Rapidite % 131
  7. 7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME 6 5 2 4 1.5 Flexural Strengt in Mpa Tensile Strength in Mpa 2.5 1 PCC 0.5 Rapidite 3 2 PCC 1 Rapidite 0 0 0 0.5 1 1.5 2 0 0.5 1 1.5 2 Rapidite % Rapidite % G5: Variation of 28 day tensile strength with Rapidite % G6: Variation of 28 day flexural strength with Rapidite % INFERENCES From the study of Graph G1 it is clear that by adding Rapidite the 7 day compressive strength decreases when compared to the plain concrete casted at the same temperature. Peak values of compressive strength of PCC and Rapidite castings are 20.5 and 18.21 respectively. So, the percentage decrease in strength is about 11% at maximum values. From Graph G2 it is clear that for 7 day tensile strength of cylinders Rapidite castings have higher peak strength at about 1.2% rapidite dosage as compared to PCC castings. However, the average strength decreases with dosage of rapidite. From Graph G3 it is evident that the flexural strength in general decreases with usage of Rapidite. However, the flexural strengths are almost equal at a rapidite dosage of 1%. G4 shows general decrease in compressive strength. However, the decrease in peak 28 day compressive strength for the concrete with Rapidite is about 15% which is greater than decrease in peak compressive strength of 11% for 7 day compressive strength. In G5, Tensile strength is decreased. However, at exactly 1% dosage of rapidite the Tensile strengths are equal of the PCC and concrete with Rapidite. The 7 day tensile strength at 1% Rapidite dosage was however, greater for Concrete with rapidite as that of PCC. In G6, A very little decrease in 28 day Flexural strength occurs with usage of rapidite from 1.2% to 1.4% dosages of rapidite. From, exactly 1.2% to 1.4% dosages of rapidite the flexural strengths of PCC and Rapidite castings is approximately same. However, the decrease in flexural strength for rapidite casting is about 73% at the rapidite dosage of 1.6%, which is quiet high. 132
  8. 8. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME CONCLUSIONS After comparing the various test results at 7 days and 28 days we can see that there are varied responses of concrete added with accelerating admixture Rapidite. Following conclusions were drawn: • There is a general decrease in Compressive strength (7day as well as 28 day) with usage of accelerating admixture rapidite as compared to PCC. The peak value of 7 day compressive strength was obtained at 1.2% but was still less than the peak value of PCC by about 11%. The peak value 28 day compressive strength was also obtained at 1.2% rapidite dosage but it was lesser than that of PCC by about 15%. So, the decrease in compressive strength is substantial. • The comparison of tensile strengths of PCC and Rapidite castings shows varied results at different rapidite dosages. The 7 day tensile strength of Rapidite casting is higher than that of PCC from 0.8% to 1.2% rapidite dosage and then it is lesser than PCC from 1.2% to 1.6% rapidite dosage. The maximum value of 7 day tensile strength is 0.8% higher than that of PCC. The 28 day tensile strength is in general lesser for rapidite castings as compared to PCC but are equal at 1% rapidite casting. • Flexural strength of Rapidite casting is in general lesser than that of PCC castings at both 28 day and 7 day ages. However, the 28 day flexural strength is almost equal for concrete with rapidite and PCC from rapidte dosages of 1% till 1.2%. Also, the peak values of 28 day flexural strengths are equal of about 4.9 Mpa. • Slump tests revealed that there is an increase in workability. Workabillity was increased with usage of rapidite at every dosage other than at 0.8%. There is a decrease of workability 0.8% rapidite dosage by 17.4%. At 1%, 1.2%, 1.4% and 1.6% rapidite dosages there is an increase in workability by 9.3%, 18.6%, 4.76% and 5.55% respectively as compared to the workability of PCC at same conditions. RECOMMENDATIONS After seeing the results of various tests it can be concluded that Usage of Rapidite has Adverse effects on various strengths of concrete at higher temperatures of around 20 degree celcius. Although, its usage shows increase in Workability but that increase in workability can be achieved by adopting other means which will not decrease the strengths at the same time. Hence it is not recommended to be used at higher temperatures of around 20 degree celcius. REFERENCES Books 1) A.M.Neville., Properties of Concrete., 4thEd.,Pearson Education., New York. 2) M.S. Shetty., Concrete Technology., 6thEd., S. Chand publishing., New Delhi. I.S Codes 3) IS 9103: 1999, Concrete Admixtures, First revision, Bureau of Indian Standards. 4) IS 9013: 1978, Method of making, Curing and determining compressive strength of accelerated-cured concrete test specimens, Bureau of Indian Standards. Web Pages and On-line Material 5) <http://civilblog.org/2013/05/10/compressive-strength-test-of-concrete-is516-1959/> 6) <http://www.hatricproducts.com/?file=kop8.php> 133

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