Optimization of Mortar Phase in Concrete Using Particle Packing Concept

Transcription

1 World Applied Sciences Journal 24 (6): , 201 ISSN IDOSI Publications, 201 DOI: /idosi.wasj Optimization of Mortar Phase in Concrete Using Particle Packing Concept P. Gomathi and A. Sivakumar Structural Engineering Division, VIT University, Vellore 62014, India Submitted: Jul 2, 201; Accepted: Aug 12, 201; Published: Aug 29, 201 Abstract: Concrete mix design involves determination of relative proportions of powder contained in the binder system, granular aggregates and water. The theory of particle packing (TPP) concepts can be used for rational proportioning of concrete mixtures analytically based on the measured properties of individual ingredients of concrete. In this regard, Dewar s concept on the TPP developed for binary particulate mixtures (BPM) is discussed in this paper with special attention to mortar systems. A number of mortar mixes were prepared manually by mixing different proportions of Portland cement and sand for each mixes, for which the quantity of water required to achieve the desired level of workability is measured. The test data presented in this paper indicates that optimized values of mortar proportions were found to be feasible using TPP. Key words: Concrete mix design Dewar s Concept Mortar Particle packing INTRODUCTION studies have been conducted on particle packing [2, 5-7]. The main issues of the research were the possibilities of Concrete mix design is a process of selecting suitable choosing the correct type of aggregate for the optimal ingredients of concrete and to determine their relative concrete proportions leading to reduced porosity of the proportions with the objective of producing concrete of hardened mortar with higher compressive strength of the required strength and durability as economic as possible. concrete [2]. Fuller and Thomspon investigated the Theoretically there are many possibilities for arriving the importance of the size distribution of aggregates and the composition of concrete mixtures. The advantage of using properties of concrete on the basis of packing of the packing concept is that it is based on a correct constituent materials [8]. The experimentally based physical mechanism in contrast to conventional methods diagrams of packing of aggregates and these diagrams of concrete mix design. It is observed by several authors represent the triangular packing diagrams [8, 9]. Powers that the particle packing models could be used for the also has mentioned in his extensive work with regard to optimization of concrete ingredients [1, 2]. The present concrete mix design on the basis of packing concept [5]. study considers Dewar s model applicable for Binary The classical work performed by Powers and co-workers Particulate Mixture (BPM) and describes experiments to resulted in empirical analytical relationships for the validate the model formulation suggested by him for the estimation of the void ratio of concrete mixtures [2, 5]. required mortar content to be used in concrete. A number of mortar mixes were prepared manually by mixing Scope and Significance of the Present Study: The scope different proportions of Portland cement and sand. of this work is related to the studies on the applicability of For each of the mixes, the quantity of water required to theory of particle packing (TPP) to mortar system. achieve a pre-selected level of workability was measured. Experimental studies on mortar were carried out for The optimum proportion of ingredients to produce mortar different proportions of sand (coarser fraction) and with minimum voids was identified by the optimization cement (finer fraction) to determine their optimum process. combination at which maximum packing occurs. The analytical data for drawing the theoretical Void Ratio Review of Literature: Particle packing approach for Diagram (VRD) was computed using the empirical concrete mix design is increasingly accepted as more equations developed by Dewar []. Also, the validation of rational than the conventional methods [, 4]. Many model was done by comparing the data generated by Corresponding Author: P. Gomathi, Structural Engineering Division, VIT University, Vellore , India. Tel:

2 World Appl. Sci. J., 24 (6): , 201 empirical models with experimental data. It was observed Table 1: Sieve analysis of aggregates that optimisation of mortar is feasible using TPP. Hence Sieve size, di (mm) this study helps to determine the optimum sand to cement ratio for the given set of ingredients to produce mortar with minimum voids and this would relate to the water demand. The TPP method of determination of ingredients is more rational as it considers many properties of ingredients such as fineness and water demand of cement and the actual sieve analysis of aggregates. These properties are not explicitly considered in many Aggregates: conventional mix design procedures. River sand conforming to zone I Details of Experiment Methodology Specific gravity of sand 2.40 Properties of Materials Used: Fineness modulus.51 Mean size Cement: Type: OPC 5 Grade Standard consistency 2.5% Specific gravity of cement.15 Mean size of cement Mean size of cement is determined using fineness value of cement. Fineness is simply the reciprocal of mean size, assuming that shape is constant. Fineness calculated by Blaine s air permeability test can be converted to mean sizes by the following equation. Mean size (in mm) = K f/ (RD p*f) (1) Weight fraction retained, f i Mean size of aggregates (fine and coarse) is calculated by grading them through sieve analysis (Table 1). When a granular mixture material consists of particles of different sizes, the mean size to represent all particle sizes is computed by ns i 1 i log( d) = f *log d = i D mean is the average particle size f i is the volume fractions of particles with mean sizes. D mean or D 0 = 0.87mm () Rd p = Relative density of the powder 2 2 F = Fineness (Blaine) in m /kg [00 m /kg] K f = Constant [14] Mean size (in mm) = mm Void Ratio: The void ratio U for cement can be estimated 1 from the Vicat test using the following formula. U = (RD *SC+a ) / (100-a ) (2) 1 P P P RD P = Relative density of the powder [dimensionless parameter] SC = Water content of the paste at standard consistency in the vicat test, calculated as a percentage of the mass of cement. a P = Air content (%) in the paste, say 1.0 U 1 = Loose Bulk Density (LBD): LBD will determined by loose filling of mould with aggregate by pouring it into mould manually from a vertical distance of about 00 mm above the top of steel mould. LBD = W/V (kg/m ) (4) W = Weight of aggregate required to fill the cylindrical mould (kg). V = Volume of cylindrical mould (m ). LBD = 1478 kg/m Void Ratio: The void ratio of aggregate can be calculated from its bulk density in air and its relative density. The formula for calculating the void ratio, U 0 of an aggregate is: U = [(1000*RD)/LBD]-1 (5) 0 747

3 RD = Relative density of the aggregate LBD = Loose bulk density of the aggregate U 0= 0.62 World Appl. Sci. J., 24 (6): , 201 Selection of Slump Test for Water Demand Studies of Mortar: The void content of the mortar was determined by water demand studies. Slump test which is commonly adopted method to test the workability and was used in the present study to assess the water demand of mortar. Cement paste of standard consistency in the vicat s test Fig. 1: Experimental and Analytical VRD plot for mortar produced a slump in the order of 50mm. Also the commonly selected value for concrete trials and reference n = V S1/V S = V S1/ (V S1+V SO) (6) purpose by the ready mixed concrete industry is 50 mm slump. Dewar suggested that the mortar of concrete of U = V V/V S= (V W+Va)/V S (7) 50 mm slump simulated by the theory do not need major adjustment to account for aggregate contents V S1 = volume of finer fraction (cement) estimated from LBD []. For these reasons, 50 mm was selected as the reference slump for simulation of pastes = (W ce/g ce) (8) and mortar. V SO = volume of coarser fraction (sand) Preparation of Mortar: Known weight of saturated surface dried sand and cement were hand mixed in dry = W sa /G sa (9) state in a known volume of the container. Then the required quantity of water (determined by trial and error) was added to the dry mix and mixing was done manually G ce = Specific gravity of Portland cement. till homogeneous mix was attained. G sa = Specific gravity of sand. W ce = Weight of cement. Measurement on Mortar: The slump cone was filled in W sa = Weight of sand. layers with the prepared mortar mix. The layers were V W = Volume of water. compacted by applying 25 blows to each layer with a V a = Volume of air is assumed as 4% of total volume. tamping rod. After removal of slump cone, the subsidence of mortar was recorded carefully in terms of slump value Experimental plot of VRD is obtained by taking fine for the various mortar containing different water content fraction n as abscissa and void ratio as ordinate. The and was continued till the reference slump of 50mm was value of n varies from 0 to 1. The set of co-ordinates (n, U) achieved. from experimental data (Table 2) are plotted in the VRDs. Theoretical VRD can be drawn using empirical equations RESULTS AND DISCUSSION based on TPP advocated by Dewar [] (Figure 1). The validations of Dewar s empirical equations with the Computation of Voids Ratio of Mortar System and experimental results were found to be highly adequate. Construction of VRD Plot: The voids content of the mortar is the space occupied by mixing water and Optimisation of Mortar System: From the theoretical plot entrapped air during mixing. The concept of particle of VRD it is observed that at the change over point D packing and the introduction of various parameters used (n=0.29) the void ratio is minimum (U=0.42) (Table ) for the construction of VRD are explained in discussions. and hence D is the optimum point for the sand and The following equations for voids ratio (U) and fine cement used. At this optimum point, the packing is fraction (n) (explained in discussions) are used for the maximum and hence the amount of water required is less. construction of experimental plot of VRD for mortar When mortar is made with such an optimum proportion (Fig. 1). (C: S = 1:1.9), it can result in more strong and durable mix. 748

4 World Appl. Sci. J., 24 (6): , 201 Table 2: Computation for Experimental VRD plot of Mortar system Coarser Particulate Finer Particulate Voids VRD Parameter Weight of sand, Volume of Sand, Weight of cement, Volume of cement, Volume of water, Volume of air, Total Volume Fine fraction, Void ratio, WS (kg) Vsa (m ) W C(kg) V C(m ) V W(m ) Va (m ) (m ) n U Table : Computation for theoritical vrd plot of mortar system Emprical constant Change over point Spacing factor, m Kint KP U0'' Z U1'' N Un A B C D E F Infinity This optimisation process can be extended to concrete (1 + U 0)1 Z = Kint + 1 Kint rkp (12) system by considering it as a BPM of coarse aggregate (coarser fraction) and mortar (finer fraction). where K and K are empirical constants Concept of Particle Packing Theory: The basic concept d r = 1 of particle packing is that when two particulate materials d0 (1) of different particle sizes are mixed together, the volume of voids in their mixture is lesser than the voids volume in U0'' = (1 + U0)(1 + m*r) 1 (14) the individual components. This is because of the filling of smaller Particle in the voids of larger particles. Beyond 1 + U0 '' a particular proportion of finer particles instead of filling, 1 (1 + U0) (15) m = * 1 particle interference occurs resulting in additional voids. r In any binary particulate material (BPM) the coarser particles, (with mean particle size d and voids ratio, 0 U 0=V 0/V S0) are mixed with another particulate material with Dewar had confirmed that the Voids Ratio Diagram finer particles (having mean particle size, d 1 and voids (VRD) showing the Voids Ratio (VR), U as the ordinate ratio U 1=V V1/V S1) in the ratio n, defined as the fraction of and the finer fraction, n as abscissa, can be drawn for finer particles. the range of n=0 to n=1 respectively. The parameters required to construct VRD are size ratio (r), spacing n = VS1(VS1 + VS0) (6) factors (m and Z) and void ratio of coarser and finer fractions of binary mix (U 0 and U 1). The VRD consists of V S1, V S0 = solid volumes of finer and coarser generally straight lines joining the five change over particles points, A, B, C, D, E & F which relate to the inherent Then, the voids of the BPM are computed by interference of the particle affecting the void ratio of the following equations: binary mixture (Fig. 2). The actual shape of the curve in the VRD depends upon the parameters, r, U 0 and U1 U = nu1'' (10) (Fig. 2). The importance of the VRD plot lies with the fact [(1 + U1) U0''] U1'' = [(1 + U1) U0''][1 + U0'' (1 + Z)] 1 int P that it is not necessary to conduct real time experiments to (11) arrive the quantities of mixtures of particulate materials, instead, it is sufficient to know only two parameters, (I) 749

5 World Appl. Sci. J., 24 (6): , 201 The application of Dewar s particle packing concept best use for arriving the right proportions of self compacting concrete to held a maximum viscosity with minimum shear reinforcement with required for self compacting. REFERENCES Fig. 2: Concept of Theory of Particle Packing 1. Rajamane, N.P., Indu Siva Ranjani, B.H. Nagabhushana Rao, J. Annie Peter and mean size of particles and (ii) Voids Ratio (VR), of each of Gopalakrishnan, Use of theory of particle two particulate materials in order to construct the packing for estimation of mean particle sizes of fly complete VRD []. ash and silica fume relative to Portland cement. Proc. The fine fraction n, corresponding to minimum VR of Of Second National Conference on Advances in the mixture can be obtained from the VRD; this Concrete Technology. corresponds to the point, selected from the change over 2. Golterman, Vagn Johansen and Lars Palbol, points (COPs) points A to F giving the minimum of VR. Packing of aggregate: an alternative tool to determine This means that after computing the VRs, U A, U B, U C, U D, the optimal aggregate mix. ACI Materials Journal, U Eand U Fat the COPs of A, B, C, D, E and F, respectively, pp: the value of Umin is found by:. Dewar, J.D., Computer modelling of concrete mixtures, E & F. N. Spon, pp: 256. Umin = Minimum of (U A, U B, U C, U D, U E, U F) 4. Larrard, F.D.E. and T. Sedran, Optimisation of Ultra-High Performance Concrete by the Use of a The values of n at points A to F can be found out Packing Model. Cement, Concrete and Aggregate, by the equation: 24(6): Power s, T.C., The properties of fresh concrete U 0'' n = (16) John iley & sons, Inc, New York. ( U0'' + U1'' + 1) 6. Kantha Rao, V.V.L. and S. Krishnamoorthy, 199. Aggregate Mixtures for Least-Void Content for Use where the terms U 0'' and U 1'' are the apparent values of the in Polymer Concrete. Cement, Concrete and materials for the point on the VRD and their values are Aggregate, CCAGDP, 15(2): calculated using equations (11) to (16). 7. Thygesen, E. and F.L. Kronholm, Packing of sand and stone materials in concrete. (in Danish), CONCLUSIONS Dansk Beton nr, pp: Glavind, M. and E.J. Person, Packing The propose study enumerates the various Calculations Applied for Concrete Mix design. applications of the particle packing concept for Proceedings creating with concrete, University of arriving the binary mixtures which can be optimum Dundee. composition for ternary blended concretes. 9. Suenson, E., Building Materials II: Stone, Water demand studies on mortar can be used to Pottery, Mortar, Concrete, Artificial Stone, Glass, construct the Void Ratio Diagram of mortar by (in Danish). considering the mortar as BPM having sand as coarser fraction and cement as finer fraction and voids representing the water requirement of matrix. Optimisation of mortar system is feasible using TPP proposed by Dewar. The mortar proportion of 1:1.9 is observed to produce mix with minimum voids and hence it can be recommended for applications where strong and durable mix is required. 750