PACKING DENSITY OF SELF COMPACTING CONCRETE USING NORMAL AND LIGHTWEIGHT AGGREGATES

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 4, April 217, pp Article ID: IJCIET_8_4_129 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed PACKING DENSITY OF SELF COMPACTING CONCRETE USING NORMAL AND LIGHTWEIGHT AGGREGATES Padmaja P Kumar Student, M. Tech Structural Engineering, School of Civil and Chemical Engineering, VIT University, Vellore 63214, Tamil Nadu, India Rama Mohan Rao. Pannem Associate Professor, Centre for Disaster Mitigation and Management, VIT University, Vellore-63214, Tamil Nadu, India ABSTRACT Based on the available literature, a simple method was adopted to calculate the packing density and thereby reduce the void content of aggregates by optimising the packing of aggregates, by using two different sizes of coarse aggregates and fine aggregates. In this study provides an understanding on the way in which the shape of aggregates affects the properties of SCC. The fresh, hardened and durability properties of SCC with normal and lightweight fly ash coarse aggregates are compared. The mix with fly ash aggregates is found to have better fresh concrete properties due to round shape of aggregates. For the mix after packing of aggregates is found to have better mechanical and durability properties than all the other mixes. Key words: Lightweight Fly Ash Coarse Aggregates, Optimisation, Packing Density Cite this Article: Padmaja P Kumar and Rama Mohan Rao. Pannem, Packing Density of Self Compacting Concrete Using Normal and Lightweight Aggregates. International Journal of Civil Engineering and Technology, 8(4), 217, pp INTRODUCTION Self - compacting concrete is a concrete which can flow under its own weight without segregating and can fill the formwork as well as spread into reinforcement without providing any mechanical vibration or compaction. During the 18 th century, durability of structures was the major concern in Japan. In order to have durable structures proper compaction should be provided but, due to the lack of workmanship the quality of construction was affected. There occurred the need to produce a new type of concrete which can spread freely without any consolidation called Self Compacting Concrete, this was first suggested by Okamura in Workability studies were proposed later by Ozawa and Maekawa in 1988 at University of Tokyo editor@iaeme.com

2 Padmaja P Kumar and Rama Mohan Rao. Pannem 1.1. Research Significance The Cement Industry solely contributes to 7 % of carbon dioxide released into the atmosphere. These anthropogenic activities result in greenhouse effect and global warming. One solution to this problem is to recede the use of cement by replacing some part of cement with cementitious materials like Ground Granulated Blast Furnace Slag (GGBS), Silica Fume (SF) or Fly ash (FA). SCC mixes will include large quantities of powder content in order to have required paste to provide the required flowability. By introducing a new concept like Packing density, the powder content can be optimised. The main focus of this project is to introduce the packing density concept to improve the properties of SCC and optimise the consumption of cement and supplementary cementitious materials and, produce economical and sustainable concrete thereby paste content can be reduced which results in less shrinkage Packing density According to Griffith theory, voids are strength determinatives. And voids are said to be origin of stress concentration, therefore by reducing the voids the particle packing density can be improved. Monosized particles tend to produce more voids hence the paste required to fill the voids and the extra paste required to produce flowability will be more. So, the basic principle in packing phase of aggregates is to reduce the voids, hence a lot more amount of paste is available for flowability. In this study, two different size of coarse aggregates are mixed with fine aggregate and the packing density is calculated. From packing density, the void content is calculated and from trials the paste content is optimised Literature review A simple mix design for producing good quality SCC for medium strength concrete was first developed by Nan Su, with fine aggregates of 54-6 % [11]. Later on, this method was modified to have low cement content, for that the packing factor was calculated first and then cementitious materials were filled into the voids [12]. There are some variations in dry packing density which is obtained and the packing density obtained from different packing model. This variation can be reduced by using wet packing method which have been used to determine the packing density of blended fine aggregates under wet condition and the packing density was found to be higher than that obtained in dry packing [6]. The properties of SCC depend on paste content, amount of aggregates, Gradation of aggregates. With same Packing density, the fresh concrete properties depend on the selection of proportion of aggregates and the mechanical properties are not affected. Larger variations in void ratio is influenced by packing of aggregates and small variations by powder phase. A simple method to obtain packing density was proposed and ternary packing diagram was developed by MATLAB [5]. A mix design which is cost effective when compared to other mix designs and the SCC mixes can be attained without any extensive trials and testing. It consists of 3 stages, in first stage optimisation of paste and granular skeleton, in second stage quantity of materials is calculated per m 3 of concrete and in third stage parameters are adjusted like paste volume, water to powder ratio and so on. For optimising paste he have conducted Marsh cone test and Mini slump test to finalise the admixture and cement quantities. And the granular skeleton was optimised by methods in ASTM C29 [2] editor@iaeme.com

3 Packing Density of Self Compacting Concrete Using Normal and Lightweight Aggregates 2. MATERIALS 2.1. Binder materials OPC53 grade cement from Zuari cement with Specific gravity of 3.15 is used. In the present study, 5 % of cement is replaced with supplementary cementitious materials in that 5 %, 35% of GGBS and 15% SF is used. Ground Granulated Blast Furnace Slag (GGBS) and Silica Fume (SF) from Astra chemicals with specific gravity 2.85 and 2.63 respectively is used Normal aggregates Coarse aggregates of two different sizes mm with Specific gravity 2.66 and mm with Specific gravity 2.69 were used for the study. And Fine aggregates having size less than 2.36 mm were used Lightweight coarse aggregates Class F Fly ash was used for preparation of Fly ash coarse aggregates. Then these pellets were sieved and the aggregates having sizes mm with SG and mm with SG were selected for this study Preparation of fly ash pellets Based on the curing regime there are three methods for preparation of lightweight aggregates, they are sintering, autoclaving and cold bonding techniques. 2% Ca(OH) 2 and 8% OPC53 grade is added to fly ash by weight Fly ash & binder are dry mixed for 2 minutes 22 % of Water with Ca(OH) 2 is sprayed in to it after 3 minutes pellets are formed Fresh pellets were kept at room temperature for 24 hours Water cured for 28 days The purpose of adding Calcium hydroxide is that it reacts with silica present in fly ash and produces C-S-H gel which contributes to better initial strength, improved rate of hydration, and agglomeration [15] Tests on aggregates Aggregate Impact tests and Aggregate Abrasion tests was conducted on normal and fly ash aggregates and the Aggregate Impact value was found to be 16.2 % and % respectively this value is less than 45 % (permissible value as per IS: ). And aggregate abrasion value was found to be 22.3 % and 99 % respectively. For fly ash, the abrasion value exceeds the permissible value of 6 % 2.4. Superplasticizer Auramix 4 is poly carboxylic ether based superplasticizer used in SCC, in accordance with IS from FORSOC chemicals was used for the present study. The density of superplasticizer is 1.9 kg/l, it contains 4% VMA editor@iaeme.com

4 Padmaja P Kumar and Rama Mohan Rao. Pannem 3. EXPERIMENTAL PROGRAM In this study, SCC with mm was used as control mix and it is compared with SCC after optimising the aggregate content but with same paste content as normal SCC. Then a SCC mix after optimisation of paste is obtained from different trials. SCC with light weight aggregates is also prepared Packing of Aggregates For optimising the aggregates, experimentally packing density of aggregates was calculated [7] Procedure to find optimum packing density: Weight of coarse aggregate and sand was taken to fill a 1 L container. Coarse and fine aggregates were taken in different proportions of volume and it is mixed manually till it becomes a proper blend And it is filled in top container and then the trap door is opened. 8L container which is kept below gets filled instantaneously, after levelling it is weighed and bulk density and packing density was calculated. The Bulk density for different proportion of aggregate was obtained and is calculated as the total weight by volume of container. Similarly, the packing density of different proportion of aggregates can be written as, Packing Density = ( + + ) Void Content = 1 Packing Density where, M1, M2, M3 - weight of each aggregate G1, G2, G3 - Specific gravity of different aggregates V volume of the container Bulk density 18 BD 1 BD 2 Bulk density (kg/m3) Proportion of aggregates Figure 1 Bulk density of aggregates editor@iaeme.com

5 Packing Density of Self Compacting Concrete Using Normal and Lightweight Aggregates Packing density Packing density PD2 PD Proportion of aggregates Figure 2 Packing density of aggregates.6.55 Void content VC2 VC 1 Void content Proportion of aggregates Figure 3 Void content of aggregates Figure 4 Experimental Points of Packing density determination BD1, PD1, VC1 indicates the Bulk density, Packing density, Void Content of coarse aggregates and sand. The void content for 2 coarse aggregate was minimum at proportion 7:3 and was found to be After mixing sand to this mixture in different proportions the void content was found to be.358 at proportion 6: 4 (CA: FA). In this 6 percent of coarse aggregate, 7 percent is mm aggregates and 3 percent is mm editor@iaeme.com

6 Padmaja P Kumar and Rama Mohan Rao. Pannem Mix 3.2. Mix design of SCC mixes Modified Nan Su method is used for mix design of control mix with M 25 grade i.e. mix with mm aggregates. As per ACI 237R -7 the permissible limit for water to cementitious (w/cm) ratio for SCC is in the range Different trials were conducted with w/cm ratio.32,.325and.33. And.325 was adopted as the control mix (NSC). The second mix (PDSC) was adopted after incorporating the packing of aggregates, this mix was designed with the same paste content as NSC and then trials were carried out with different w/cm ratio. The Slump was obtained for w/cm of.32 for PDSC mix Optimisation of Paste content Paste include the Binder materials, Superplasticizer and water. Third mix (OPSC) was adopted after optimisation. For the first trial to obtain this mix the paste content was roughly calculated from the formula given below. Here the Air content in the mix was assumed to be about 1.8 %, as per ACI 237R-7 the air content can be -2 %. After substituting these values in the formula and adding 1 % extra paste for flowability. So, the Paste content was obtained as 33 %. Paste content = 1 Packing density - Air content + (1-4%) But, from the guidelines of ACI 237R 7 the paste content varies from 34 %- 4%. So, for the first trial mix the paste content adopted was 35 %. Trials were carried with varying paste content and mix with 36 % paste content with proper flowability, filling ability and passing ability was adopted as the optimised paste. The fourth mix (FDSC) was SCC using fly ash coarse aggregates, 2 different fly ash aggregates were mixed in the same proportion as that of normal aggregates i.e. 6: 4 proportion of fly ash aggregates and sand and in that, 6 percent fly ash aggregates 7 percent fly ash aggregates with mm and 3 percent mm sizes was adopted. Paste content same as normal SCC was used for calculating the mix design of FDSC Cement (kg/m 3 ) GGBS (kg/m 3 ) Table 1 Mix Proportion of various mixes SF (kg/m 3 ) Water (kg/m 3 ) SP (l) CA (kg/m 3 ) mm mm Sand (kg/m 3 ) NSC PDSC OPSC FDSC Mixing Procedure The aggregates and powder materials were first filled in mixer and then dry mixing was carried out for 2 minutes. After proper blending of this mixture, around one fourth of total water was added initially into the mixer and then mixed. After that, rest of the water with superplasticizer was added to mixer and mixed for 5 minutes. While using fly ash aggregates they should be soaked in water for 3 minutes and then surface dried prior to mixing with other materials. 4. RESULTS AND DISCUSSIONS While selecting control mix, the mix with w/cm ratio.32 did not provide the required slump flow as per ACI 237R 7, and mix with w/cm ratio.33 showed signs of segregation, so the mix with w/cm ratio.325 was tested and appropriate slump was obtained, hence this was taken as control mix editor@iaeme.com

7 Packing Density of Self Compacting Concrete Using Normal and Lightweight Aggregates 4.1. Fresh Concrete Properties Table 2 Fresh concrete Properties Tests Property NSC PDSC OPSC FDSC EFNARC Limit Slump flow (mm) Filling ability T 5 (s) Filling ability J ring (mm) Passing ability VSI Stability L box (h 2/h 1) Passing ability V funnel (s) Filling ability V funnel T5 minutes (s) Segregation Resistance Mechanical Properties Compressive Strength (N/mm 2 ) day 14 day 28 day NSC PDSC OPSC FDSC Figure 5 Compressive strength values Split tensile Strength (N/mm 2 ) day 14 day 28 day NSC PDSC OPSC FDSC Figure 6 Split tensile strength values editor@iaeme.com

8 Padmaja P Kumar and Rama Mohan Rao. Pannem Flexural Strength (N/mm 2 ) NSC PDS OPS FDS C C C Flexural Strength Figure 7 Flexural Strength of 4 mixes after 28-day water curing The 28-day compressive, split tensile and flexural strength is maximum for PDSC and is found to be 55.65, 3.29 and 7 N/mm 2 respectively. This is because the packing of aggregates has improved the properties. Mix after optimisation of paste has better properties than control mix. FDSC mix has less strength because the fly ash pellets are having less strength Durability Properties Water Absorption tests and Sorptivity For water absorption, the specimens are immersed in water for 24 hours after oven drying for 24 hours and then the weight and compressive strength is noted. In case of Sorptivity the specimen of sizes 1mm diameter and 5mm height was oven dried for 24 hours and covered with sealant and placed in water for 5 hours and the change in weight in every.5 hours is noted. % increase in Weight NS PD OP FD C SC SC SC Water absorption Figure 8 Water absorption editor@iaeme.com

9 Packing Density of Self Compacting Concrete Using Normal and Lightweight Aggregates Infiltration rate (mm/min.5 ) NSC OPSC PDSC FDSC.5 hr 1 hr 1.5 hr 2 Hr 3 hr 4 hr 5 hr Figure 9 Sorptivity Acid Resistance The specimens after 28 days curing is kept in solution with 2% H2SO4 and weight at 7, 14 and 28 days is noted and compressive strength at 28 days was tested. 25 % Decrease in Strength NSC PDSC OPSC FDSC H2SO Figure 1 Decrease in Strength % loss in weight day 14 day 28 day NSC PDSC OPSC FDSC Figure 11 Mass loss editor@iaeme.com

10 Padmaja P Kumar and Rama Mohan Rao. Pannem 5. CONCLUSION FDSC mix is having good fresh concrete properties as the aggregates are rounded VSI value of FDSC mix indicates that it is less stable mix with slight aggregate pile at centre, OPSC and NSC MIX are highly stable as there is no segregation and for PDSC, VSI value is 1 so it is stable as there is no aggregate pile at centre of slump flow Mix with Fly ash aggregates has less stability hence it can be concluded more paste content is required for this mix, than the mix packed with normal aggregates. Mechanical Properties of mix with fly ash aggregates are slightly lower than normal mix as fly ash aggregates have low strength For PDSC the % increase in compressive, split tensile, and flexural strength is 9.5 %, 18.77%, 12% respectively. The PDSC mix was found to be more durable as the voids have reduced less permeability of undesirable materials is reduced. FDSC mix is found to be less durable as voids is more and the fly ash pellets are sensitive to these attacks The mixes with same paste content, after packing of aggregates have shown an improvement in fresh, hardened and durability properties And mix after optimisation of paste have resulted in reduction in reduction in consumption of materials and shows improved properties compared to control mix REFERENCE [1] American Concrete Institute (ACI), (27) Self-Consolidating Concrete, ACI 237R -7 [2] G.Rodriguez de Sensale, Rodriguez Viacava and A. Aguado, Simple and Rational Methodology for the Formulation of Self-Compacting Concrete Mixes, ASCE (215) 28 pp : [3] IS , Specification for coarse and fine aggregates from natural sources of Concrete, BIS, New Delhi. [4] EFNARC, Specification and guidelines for self-consolidating concrete, European Federation of Producers and Applicators of Specialist Products for Structures, (22) [5] Prakash Nanthagopalan, Manu Santhanam, An empirical approach for the optimisation of aggregate combinations for self-compacting concrete, Materials and Structures (212) pp: [6] A.K.H. Kwan, W.W.S. Fung, Packing density measurement and modelling of fine aggregate and mortar, Cement and concrete Composites, (29) 31 pp: [7] Yun Wang Choi, Yong Jic Kim, Hwa Cheol Shin, Han Young Moon, An experimental research on the fluidity and mechanical properties of high-strength lightweight selfcompacting concrete, Cement and Concrete Research (26) 36 pp: [8] Jegathish Kanadasan, Hashim Abdul Razak, Mix design for self-compacting palm oil clinker concrete based on particle packing, Materials and Design (214 ) 56 pp: 9 19 [9] Yong Jic Kim, Yun Wang Choi, Mohamed Lachemi, Characteristics of self-consolidating concrete using two types of lightweight coarse aggregates, Construction and Building Materials (21) 24 pp:11 16 [1] Nan Su, Kung-Chung Hsu, His-Wen Chai, A simple mix design method for selfcompacting concrete, Cement and Concrete Research (21) 31 pp: editor@iaeme.com

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