The packing efficiency calculated with the amount of excess water. measured within the equivalent rigid draft area..33 Figure 16. A). The collapsing location within the entire ternary plot. packing efficiency measured within the equivalent rigid draft area. The change in packaging efficiency in percent from wet to dry and. normalized for the dry packing efficiency of all assemblies therein. the equivalent rigid depression area..35 Figure 18. A) The PED data extrapolated from the full matrix, (B) The PEW.
The pore saturation volume is determined based on packing efficiency. and the excess water content window calculated for equivalent stiffness. It was also observed that the measured improvement in packing efficiency associated with the addition of water to a dry system was also 3%, exactly the excess volume needed for equivalent stiff slump.
INTRODUCTION
The packing efficiency of the aggregate, sand and cement can affect the level of water required for flow. Changing the packing efficiency of the mixture changes the volume of liquid needed to achieve the desired level of saturation. Tap density was used to determine the dry and wet packing efficiency of the mixture.
In the extrusion process, it was found that a volume of excess water between 4-8 percent by volume (v/o) was required to flow the milled flat alumina.4 For strip casting an additional 6-12 (v/o) of additional water was ideal for suspension flow.5 Since a constant excess water window was discovered for these two treatment methods, the idea followed that a similar flow could also be predicted by the drop test. It was hypothesized that the window of excess water content for uniform decline would be constant regardless of the change in volume percentage of the mixture containing gravel, sand and cement.
LITERATURE SURVEY
General Background on Portland Cement Concrete
Concrete History
Portland Cement
Aggregate
The difference between sand and gravel is mainly based on one characteristic, which is their size. Material that can pass through 3/16 mesh or ASTM sieve size number 4 (4.75 mm) is classified as sand, while larger material is classified as gravel; however, many sand deposits contain some gravel and vice versa.
Water-to-Cement Ratio
Specific Volume Diagram
Packing Efficiency
Finally, due to the overlapping particle size distributions of the gravel and sand (aggregate) used in these experiments, it is demonstrated that these cement compositions could be considered as a binary mixture, with an observed optimum in packing efficiency at approximately 80:20 (aggregate:cement), as would be predicted for a binary packing system. Standard Test Method for Slump of Hydraulic-Cement Concrete.”3 The slump test procedure has remained unchanged since its introduction in 1922 and is still the primary method for testing the flowability of a mixture. In plastic bodies, the particle packing dictates the amount of water in the system.
A specific volume diagram is used to determine the pore volume of compacted particles and to determine the amount of additional water required for perfect flow.2 The specific volume diagram gives the saturated pore volume and associated density. In the concrete industry, the efficiency of packing coarse and fine materials, the content of cement and water required to fill the pores is critical.
Water Addition Affecting Packing Efficiency
However, proportioning mixtures has long been more of an art than a science, and this is clearly demonstrated by the variety of different methods used around the world. One of the challenges in the concrete industry is aggregate, as aggregates vary in size, shape and chemical composition depending on their location. Particle packing models are based on the concept that the voids of large particles are filled by smaller particles, thus reducing the void volume while simultaneously increasing the packing density.16 The efficiency of particle packing is affected by the number of materials within the mixture.
McGeary examined the particle packing of spherical particles of one-, two-, three-, and four-component mixtures and determined the optimal theoretical packing density.17 Typically for a single-component material, the spheres constitute ~60% to 64% of the packing volume. leaving 40% to 36% empty spaces. Schematic representation of the effect that tapping has on the volume of the system together with the addition of water.
Slump Testing
EXPERIMENTAL PROCEDURE
Raw Materials
Particle Size
Design of the Experiment
14 data points for each of the six statistical designs in Figure 6 are presented in Appendix A. An example of the compositions associated with the statistical experimental matrix along with the replicates. Ternary diagram of the six experimental designs used to determine the optimal dry packing efficiency.
Packing Density Measurement
Dry Packing Density
Rule of Mixtures (R.O.M.)
Mixing Time
Wet Packing Density
Slump Testing
Determining Water Content for Slump Test Calculations
Each of the pack efficiencies for the slump testing was extrapolated from the dry pack efficiency data. Where VB is the total volume of the batch and PE is the packing efficiency.
Slump Test Procedure
The material was first extracted from the planetary mixture and placed in graduated cylinders to measure the wet tap density. The remaining material was used to complete the slump test (measured in millimeters) which was done using a standard steel slump cone (Steel Slump Cone, Model HM-45M, Global Gilson, Lewis Center, Ohio) at the tip of a steel plate. After the drop test was completed, the material was returned to the planetary mixer and the cycle was repeated after increasing the volume of water.
Drop testing was typically completed in approximately 1 hour so that any disturbance of cement setting was not taken into account.
RESULTS AND DISCUSSION
Determining Packing Efficiency Using Tap Density
Wet Packing Density
The packing efficiency in the previous section was used to determine the amount of water required to fill the pore volume. Ternary drop matrix with measured values of wet packing efficiency and standard deviations associated with compositions. Packing efficiency is calculated by the amount of excess water measured within the equivalent solid drop region.
The ternary diagram shows that as the cement content within the structure decreases, the packing efficiency increases. The change in packaging efficiency was calculated on a percentage basis (Equation 8); normalized to dry packing efficiency. The wet packing efficiency was normalized to the dry packing efficiency for each composition and showed that the addition of water improved the overall percent packing efficiency by 3±6.4%.
Change in percent packing efficiency from wet to dry and normalized to dry packing efficiency of all compositions within the equivalent solid drop region. The ternary plot of the standard error shows that none of the predicted values differed by more than 0.5 times the standard deviation of the mean. In this study, there is a correlation between dry packing efficiency and the ideal amount of excess water needed for slip, based on the improvement in powder packing density with the addition of water.
It is suggested that this improvement in packing efficiency from a dry mix with the addition of water is related to the slump window, by producing the excess water content required for equivalent stiff slump. The slump test pore volume decreased with tamping at each of the three tamping stages (as discussed in literature review). Along this line - a 1:1 ratio of gravel to cement - the entrained air decreases with rising sand.
Slump Testing
A Shapiro-Wilks test P value of 0.7859 showed that the excess water levels required for an equivalent rigid depression were normally distributed. 21 Figure 21 shows a regression line used to determine the linear equation, 95% confidence interval, and prediction bands. This figure can be used to help predict how much excess water is needed for a specific slump, or vice versa.
At a value of 3 (v/o) excess water, the fall within the intended band of 12-42 mm is a fall similar to the 15-45 mm level defined as the equivalent solid fall. A confidence interval is defined as the area formed by the ratio of the true mean between the dependent and independent variables when the prediction band also contains the sample number from which the observations were made. Drawdown values are compared to water excess using regression analysis with confidence intervals and prediction bands.
Excess Water Content Region
The excess water required at each composition over the equivalent drop range of 15-45mm. C) The standard error ternary calculated from the excess water ternary diagram. The high packing efficiency (A) had a pore volume of 27% and the low packing efficiency (B) had a pore volume of 37%. This figure illustrates that if the packing efficiency and density of the composition, the excess water required for equivalent stiff drop can be determined.
Approaching The System As A Binary Mixture
SUMMARY AND CONCLUSION
A sink test is used to determine the fluidity of the mixture, with water added to change this consistency. Using a specific volume diagram approach, a constant window of 3 +- 2 v% excess water content was calculated for an equivalent tight subsidence region. This is a significant result that can be further developed for use by the concrete industry to make decisions about water content required for a wide variety of starting materials in the equivalent stiff slump range of 15- 45 mm.
It has been suggested that the improvement in packing efficiency is related to the window of excess water content required for equivalent hard collapse. This improvement in packing efficiency is related to the addition of water to the dry mix in the drop window, thereby creating the excess water content required for equivalent hard settling. A further conclusion of this thesis is that the concrete ternary system can effectively be treated as a binary system due to the overlap in the particle size distribution of gravel and sand.
The packing efficiency of the system did not change significantly because the cement was kept constant while the gravel and sand ratio changed. By simplifying the system as a combined aggregate (gravel + sand) plus cement, optimal particle packing was generated in a ratio of 82:18, equivalent to the predicted 80:20 from packing theory. The overlap of the particle size distributions creates a problem in generating well-packed systems.
What is poorly understood is what level of overlap, or what fraction of the particle size distributions, can be below the required 10:1 aspect ratio before packing is adversely affected. To evaluate this, it is suggested that a series of carefully constructed or scalped distributions be generated and mixed to systematically evaluate the role of particle size distribution overlap on packing behavior. Bubb, "The Effect of Ground Alumina Particle Size and Distribution on Packing Efficiency and Paste Extrusion Pressure"; MS.
