SELF COMPACTING CONCRETE FROM LOCAL MATERIALS IN NEPAL

Transcription

1 SELF COMPACTING CONCRETE FROM LOCAL MATERIALS IN NEPAL Krishna Man Shrestha (1) Jhapper Singh Biswakarma (2) (1) College off Civil Engineering, Fuzhou University, 523# Gongye Rd., Fuzhou , China (2) Genunie Engineering Technique, Kathmandu, Nepal Abstract Self compacting concrete [SCC] has basic three principles and requirements viz. filling ability, passing ability and segregation resistance. The paper reports the development of SCC in Nepal by using local materials i.e. OPC, 53 grade, Udaipur, crushed coarse aggregate (<12mm size-round), Chapagaon, sand (Two sizes: (i) 600 micron to 6mm and (ii)150 micron to 600micron),Belkhu, micro-silica, Superplastisizer (superplast- pc) and fly ash (pozzocrete-63)available in the local market in Nepal. Mix design and proportioning of SCC mixes were based on guidelines given by Okamura and Ozawa. Criteria selected for acceptance of the concrete mix as SCC were; slump value at slump flow test 650mm or higher, blocking ratio at L- box test higher than 0.8 and self level ability testing value in U- box test not grater than 30mm. In Slump flow test, the acceptable time for SCC to flow 50cm diameter is 2 to 5 seconds. The properties of SCC in fresh and hardened states were found out. Keywords: Self compacting concrete; superplastisizer; fly ash, silicafume, tests 1. INTRODUCTION Self compacting concrete (SCC) is concrete which flows under its own weight without any segregation and maintaining its homogeneity, also flows through all shapes and obstructions and needing no vibrations for compaction. Hence it can spread under its own weight through restricted section without segregation and blockage. It was first developed in Japan in the late 1980s by Professor Hajime Okamura in order to achieve durable concrete structures[8]. Such concrete is used to ensure the filling of congested sections, thin sections and area with restricted access to vibration[1]. It is also employed to improve the productivity of concrete placement and site working condition due to the elimination of vibration consolidation. Self compacting concrete consist of the same components as conventionally vibrated normal concrete which are cement, aggregate, water, additives and admixtures. Though the development and use of SCC is increasing worldwide, Nepal is a still exception country. The main aim of this research is to establish the feasibility of SCC production using easily available local row materials such as coarse and fine aggregates, cement and commercially available pozzolanic materials[3] { micro silica and fly ash (pozzocrete63) } with chemical admixture. The 61

2 second aim is to compare different proposed testing methods used for the evaluation of specific properties of fresh SCC. The other aim of the research is to find out mix design for SCC production for poorly graded crushed coarse aggregate, OPC with pozzolanic materials with super plasticizer and without the use of any type of viscosity modifying agent for the above mentioned types of sand[7]. The amount of cement was kept constant i.e.300kg /m 3 throughout all mixes. In the sequel of the paper, some experiences and test results obtained with SCC designed are presented and discussed. The flowability of concrete is not a magic but some special modification in microstructure properties of concrete[2]. 2. METHODOLOGY 2.1 Experimental Programme Materials The concrete mixes investigated in this study were prepared with a ordinary Portland cement (53 grade) produced by Udaipur cement factory, Nepal, and fly ash (pozzocrete-63) produced by Dirk India private limited, India, micro-silica, India and the superplastisizer (superplast-pc) produced by the structural waterproofing co. ltd, India. The max. size of coarse aggregate and fine aggregate were 12mm and 6mm respectively. The two sizes of sand were used which were: (1) sand (size-600micron to 6mm) and (2)sand dust (size-150micron to 600micron)[5].The latter size was used as a fine particles for a concrete. Throughout the tests, the same sources of aggregates were used Mix Proportioning, Mixing and Test Methods The concrete mixes were based on 'excess paste theory'. The trail mixes were made according to various literatures relating to production of SCC in recent years[4]. In the trail mixes, the three w/c ratios were chosen i.e. 0.58, 0.54 and And, the cement content '300kg/m 3 ' was kept constant through all the mixes. The water to cementious materials ratio was kept as per the codal provisions for concrete. The coarse aggregate to fine aggregate (including dust sand- size:600micron to 150micron) ratio were chosen as six types viz. (1) 40% to 60% (2) 42.%to58%(3)42.5% to 57.5%(4)45%to 55%(5)50%to 50% and (6) 55% to 45%.The combination of 80.5% volume of sand (size: 600micron to 6mm) and 19.5% volume of fine sand (size:150micron to 600micron) was made for all trail mixes. The all mixes were made without using any type of viscosity modifying agent.the sand and fine sand were natural sand and the coarse aggregate was of crushed type. While making the trail mixes, the total weight of concrete per m 3 was kept constant i.e kg/m 3. The test methods used for the evaluation of fresh properties of SCC were slump flow test, L-box test and U box test. Slump flow test was intended to assess the filling ability (flowability), L-box test was intended to assess the passing and filling ability and U-box test was intended to assess the passing and level ability of SCC. The standard equipments developed at lab are mentioned below. First of all for each w/c ratio, at least six types of mixes were made with six above mentioned coarse aggregate to fine aggregate ratios. Similarly, for different proportions of fly ash, silica fume and super plasticizer. Similarly, for different proportions of coarse and dust sand. The mixes were tested at each time for three different tests viz. slump test, L box test, and U box test respectively[6]. Among the various mixes, the best mixes were selected 62

3 according to the results obtained in the tests. After that, the hardened properties (compressive strength, surface finish etc.) of these mixes were found out. 3. TEST RESULTS Among the various tests, some of them were considered the best; they are as follows. Concrete mix Mix1 Mix2 Mix3 Mix4 Mix5 Mix6 Mix7 water (kg/m 3 ) cement (kg/m 3 ) coarse aggregate (kg/m 3 ) fine aggregate (kg/m 3 ) fly ash (kg/m 3 ) silica fume (kg/m 3 ) superplasticizer (kg/m 3 ) viscosity agent w/c ratio C.A./F.A Fresh properties: [1]Slump flow T50,s [2]L- box H H H2/H T20,s T40,s _ [3]U-box Difference in levels in two limbs, cm As a result of the laboratory research of SCC mixes at the above mentioned tests, the following findings were observed. 63

4 Flow (mm) W/C Ratio Relation between w/c ratio and flow Flow Velocity ( mm/sec) C.A./ F.A. Ratio Relation between C.A./ F.A. ratio and flow velocity.[w/c 0.58 ] Flow ( mm ) C.A./ F.A. Ratio Relation between CA/FA ratio and flow Blocking Ratio C.A./ F.A. Ratio Relation between CA/FA ratio and blocking ratio: [w/c 0.54] Slump flow value (mm) Time after mixing (minutes) Time (seconds) C.A/F.A. ratio T20 T40 Relation between C.A./ F.A. ratio and Relation between time after mixing and T20 and T40 time: [w/c 0.54] slump flow value [w/c 0.58,C.A./ F.A ] Relation between compressive strength and different types of mixes 50 Compressive strength (MPa) Mix No.16 Mix No.17 Mix No.18 Mix.No. 7Day strength (MPa) 28Day strength (MPa) Note: SP: Superplasticizer, SF: Silica fume Mix 16 [w/c=0.54,.a./f.a.=0.69, fly ash=206kg/m 3,SF 29.76kg/m3, SP =19.04kg/m 3 ). Mix 17 [w/c=0.58, C.A./F.A.=0.72, fly sh=200kg/m 3,SF 25kg/m3, SP=17.85kg/m 3 ).Mix18[w/c=0.54, C.A./F.A.=0.72, fly ash=205.4kg/m 3,SF 30.4kg/m3, SF=19.04kg/m 3 ). 64

5 Slump (cm) Time after mixing (minutes) Slump (cm) Time after mixing (minutes) Relation between slump vs. time after mixing for w/c =0.58 Relation between slump vs. time after mixing w/c = DISCUSSION Self compacting concrete could be prepared from the Local materials. Slump flow as high as 710 mm has been obtained with almost no segregation. With the increase in w/c ratio, the slump has been found to increase but while increasing w/c ratio above 0.58, a clear segregation could be observed. At CA/FA ratio 0.67, flow was found to be rather small but with a little change in CA/FA, the flow diameter is found to increase suddenly. At CA/FA ratio 0.65 flow was 650 mm while that at CA/FA ratio 0.72 was 700 mm. But, with further increase in CA/FA ratio flow diameter increased slightly. For w/c ratio 0.54, blocking ratio was observed to be minimum at CA/FA ratio But, for the same CA/FA ratio, with the little change in w/c ratio blocking ratio is found to be quite satisfactory. From observations, corresponding to mix 6, the fresh properties seems quite satisfactory. Though, some of the fresh properties of Mix 6 are not as good as Mix 5, but in wholesome, the slump, blocking ratio, T20,T40 being better compare to other mixes, mix proportion of Mix 6 is recommended for the mix design of SCC. 5. CONCLUSIONS From the above test results, the following conclusions can be drawn. 1. The production of SCC from local materials is possible without using any viscosity modifying agents. 2. The flow ability can be increased by increasing w/c ratio, i.e. the higher w/c ratio, the higher the flow. 3. The segregation in the flow test was found in higher w/c ratio. 4. The higher the coarse aggregate to fine aggregate ratio (C.A/F.A), generally the higher the flow and higher the segregation in flow test. 5. Flow velocity can be increased with increasing C.A. /F.A. ratio. 6. The self level-ability of mixes can be increased by reducing w/c ratio, i.e. in trail mixes, we got 4.5cm in 0.58w/c ratio and 2.1cm in 0.54 w/c ratio. 7. The blockage of concrete near the reinforcement can be reduced by decreasing the volume of coarse aggregate. 8. The level-ability of concrete can be increased with decrease in C.A./F.A. ratio, i.e. by increasing 65

6 9. percentage of fine in the concrete. 10. The passing ability can be increased with decreasing C.A./F.A. ratio or in other words by increasing paste volume. 11. The strength of the mixes can be increased with increasing the percentage of coarse aggregate. REFERENCES [1] Yin Wen CHAN, Jenn- Chuan CHERN, National Taiwan University, Taiwan. The application of SCC in Taiwan [2] P.K. Mehata and P.J.M. Monteiro, Concrete microstructure, properties and materials,3 nd Edn [3] A.M. Neville; J.J. Brooks, Concrete Technology,(Prentice hall,1987) [4] Okamura, H.; Ozawa, K.: Mix Design For Self-Compacting Concrete, Concrete Library of JSCE No. 25, June 1995 [5] Petersson, Ö.; Billberg, P.: Investigation on Blocking of Self-Compacting Concrete with Different Maximum Aggregate Size and Use of Viscosity Agent instead of Filler, Proceedings of the First International RILEM Symposium Self-Compacting Concrete, Stockholm, Sweden 1999, p [6] Shikoku Island Concrete Research Association: Report by Self-Compacting Concrete [7] Research Committee, "Self-Compacting Concrete in Shikoku Island" 2000 to 2002, [8] Okamura, H., Maekawa, K., Ozawa, K.,.High-Performance Concrete, Gihodo Publishing,