OPTIMIZATION OF ANTIFREEZE ADMIXTURE FORMULATIONS

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OPTIMIZATION OF ANTIFREEZE ADMIXTURE FORMULATIONS

Abstract

 

The objective of the study conducted was to optimize the proportions of three admixture formulations to be used for cold weather concreting and then to down select two for further research. For the purpose of the study an experimental plan was developed to conduct the optimization process based on the statistical method, Design of Experiments. The statistical data analysis program MINITAB was the tool used for generating the various runs of the experiments. The formulations were tested for the physical properties of mortars, Vicat Setting Time and Compressive Strengths. The experiments were carried out at varying temperatures in addition to varying proportions of the admixtures.

The results of the experimental runs were analyzed using the MINITAB program and a characteristic behavior pattern was developed over the range of admixture proportions for each formulation. The behavior pattern thus obtained was then used to predict the optimized proportions of the admixtures in each formulation using predefined criteria. The admixture formulations were down selected to two (one primary and one back up) based on the synergistic effects of the admixtures with each other.

Finally a detailed study of the effect of IPANEX, one of the admixtures used in the study, on the yields and its interaction with other admixtures was conducted using MINITAB. Thus the optimization of the admixture proportions was obtained through the

statistical analysis.

 

 

 

TABLE OF CONTENTS

 

LIST OF FIGURES…………………………………………………………………….x

 

LIST OF TABLES……………………………………………………………………xi

 

ACKNOWLEDGEMENTS…………………………………………………………xiii

 

CHAPTER 1 INTRODUCTION…………………………………………………………………….1

 

1.1 Background……………………………………………………………….1

 

1.2 Problem Statement………………………………………………………..2

 

1.3 Objectives…………………………………………………………………3

 

1.4 Scope of Research….………………………………………………………3

 

CHAPTER 2 LITERATURE REVIEW……………………………………………4

 

2.1. Behavior of Concrete at Low Temperatures……………………………..4

 

2.1.1. Mechanism of Hydration……………………………………….4

 

2.1.2. Effect of Low Temperatures on the Concrete Properties………6

 

2.1.2.1. Compressive Strength…………………………………6

 

2.1.2.2. Workability……………………………………………8.

 

2.1.2.3. Setting time……………………………………………8

 

2.1.2.4. Freezing Point of Concrete……………………………9

 

2.1.3. Problems of concreting at low temperatures……………………10

 

2.2. Phase 1 of the SBIR study……………………….……………………….11

 

2.2.1. Mortar Testing………………………………………………….11

 

2.2.2. Concrete Testing………………………………………………..14

 

2.3 Various Approaches of Cold Weather Concreting………………………..15

 

2.3.1. Existing Methodology and its disadvantages…………………..15

 

2.3.1.1. Existing Code Requirements…………………………15

 

2.3.1.2. Current Industry Practices ……………………………17

 

2.3.1.3. Disadvantages of the current practices……………….17

 

2.3.2. Chemical Admixtures for Cold Weather Concreting…………..18

 

2.3.2.1. Types of Admixtures and Capabilities as Antifreeze

Admixtures……………………………………………18

 

2.3.2.1.1. Superplasticizers……………………………18

 

2.3.2.1.2. Set Accelerator……………………………..18

 

2.3.2.1.3. Water Tightening Agent……………………18

 

2.3.2.2. Early use of Chemical Admixtures…………………..19

 

2.3.2.2.1. Calcium Chloride…………………………..19

 

2.3.2.1.2. Disadvantages………………………………20

 

2.3.2.3. Chloride Free Admixtures……………………………21

 

2.3.2.3.1. Nitrate based Admixtures………………….21

 

2.3.2.4. CRREL Research…………………………………….23

 

2.3.2.4.1. Pozzutec 20…………………………………23

 

2.3.2.4.2. Field evaluation and comparison of EY 11..24

 

2.3.2.4.4. Development of Antifreeze

Admixture Formulation……………………24

 

2.4. IPANEX…………………………………………………………………26

 

2.5 Design of Experiments…………….……………………………………..28

 

2.5.1 Types of Designs……………………………………………….29

 

2.5.1.1. Response Surface Design..…………………………..30

 

2.6 Summary…………………………………………………………………31 CHAPTER 3 EXPERIMENTAL PLAN…………………………………………32

 

3.1 Design Aspects………………………………………………………….32

 

3.2 Experimental Plan………………………………………………………35

 

3.2.1. Tests Conducted.……………………………………………..35

 

3.2.1.1 Vicat Setting Time Test (ASTM C 191)…………….35

 

3.2.1.2. Compressive Strength Test, Mortar (ASTM C 109) 36

 

3.2.1.3. Compressive Strength Test, Concrete .……….…….36

 

3.3 Experimentation..……………………………………………………….36

 

3.3.1 Raw Material…………………………………………………36

 

3.3.2 Storage………………………………………………………..37

 

3.3.3. Curing of Concrete…………………………………………..37

 

3.3.4 Determination of water absorption capacity………………….37

 

3.4 Conversion of Mortar to Concrete……………………………………..38

 

CHAPTER 4 RESULTS AND ANALYSIS…………………………………..…39

 

4.1 P-value.…………………………………………………………………41

 

4.2. Residual Plots…………………………………………………………42

 

4.3. Optimization Graphs………………….………………………………45

 

4.4 Performance Criteria for Optimization.………………………………47

 

4.5 Optimized Proportions of Admixture formulations..…………………48

 

4.6. Down selecting two admixtures formulations ………………………50

 

4.6.1. Down Selection……………………………………………50

 

4.7 Verification of Analytical Results for Mix 8 and Mix 12……………52

 

4.8 Conversion of Mortar Mixes to Concrete Mixes…………………….53

 

4.9 Compressive Strength and Temperature Gradient Results for

Down Selected Mixes………………………………………………..56

 

 

4.9.1. Compressive Strength Test………………………………..56

 

4.9.2. Temperature Gradients…………………………………….60

 

 

4.10. Effect of IPANEX………………………………………….………62

 

CHAPTER 5 CONCLUSIONS……………………………………………….65

 

5.1. Future Scope………………………………………………………..66

 

REFERENCES…………………………………………………………………67 APPENDIX A: Phase 2 Vicat setting time and Compressive Strength

Data for Mix 8…………………………………………………71

 

APPENDIX B: Residual Graphs, Optimization Plots and Regression Analysis

Results………………………………………………………..73

 

APPENDIX C: Contour Plots for Behavior of IPANEX……………………102

Chapter 1 Introduction

1.1 Background

Concreting during cold weather poses various challenges in terms of placement of concrete, strength gain, curing and so on. Behavior of concrete hydration changes with regards to temperature, requiring different heat inducing techniques for satisfactory placement at low temperatures. Employment of such techniques proves to be uneconomical. The cold weather experienced in certain areas for a considerable amount of time in a year reduces the construction season drastically [1]. The need to tackle the problem of reduced construction season has led to efforts of developing a concrete that is efficient at low temperatures.

Solutions such as heating enclosures and insulation have been applied to the problem of cold weather concreting since the 1930s. However these methods have not undergone any considerable amount of change until recently. Heating enclosures and insulation techniques are extremely costly, consume a huge amount of energy and also require skilled labor. The recent work focuses on the development of an antifreeze admixture to depress the freezing point of water thereby making it possible for the concrete to achieve maximum possible strength at low ambient temperatures. This reduces the cost of construction and energy required considerably.

The research undertaken by Small Business Innovation Research follows up on the earlier work conducted in the field of cold weather concreting. It aims at developing an antifreeze admixture formulation which is a combination of various admixtures. The proportions of the admixtures are optimized using statistical tools and experimentation.

1.2 Problem Statement

As mentioned in Section 1.1 the recent work in the area of cold weather concreting is focused on the development of an antifreeze admixture formulation for the placement of concrete at low temperatures in accordance with the specifications of ACI 306-02. Admixtures such as Pozzutec 20+ have been tested individually as possible solutions to the problem of cold weather concreting. Admixtures have also been tested in combination with each other. However the proportions of these admixtures were either as prescribed by the manufacturer or as mentioned in the ASTM 494 C.

The current cold weather concreting code ACI 306-02 does not provide any specific details about the methods by which the standard atmospheric conditions for concreting must be maintained at low ambient temperatures. Similarly ASTM 494 C, the standard for specifications of chemical admixtures for concrete, provides limiting values for the proportions of individual chemical admixtures to be used in concrete. However, it does not provide any clear idea about the recommended proportions for the admixtures when used in combination with each other.

A previous phase of the current research down selected three combinations of admixtures from 18 admixture combinations. The focus of the current research was to optimize the proportions of the admixtures in the formulations down selected in the previous phase of research.

 

 

 

1.3 Objectives

  • Optimization of admixture formulations identified in the Phase 1 of the project.
  • Down select to two admixture formulations.
  • Determining the effect of IPANEX on the yield and its interaction with the other factors.

 

1.4 Scope of Research

The research focuses on the optimization of the proportions of admixtures in the formulations based on the mortar properties. Three admixture formulations were downselected from a pool of 18 in the Phase 1 of the current research. A hypothesis that higher concentrations of admixtures will depress the freezing point of the water in concrete was assumed for the optimization process [2]. The proportions of the admixtures were increased and a matrix of runs with the combinations of the admixtures at various levels of proportions was developed with the help of a statistical tool MINITAB, for the optimization process. The Vicat setting time test and the compressive strength test were conducted on each of the run combinations. Analysis of the test results was performed using the statistical tool MINITAB. Based on the results of the analysis and the initially determined criteria for optimization, the optimized proportions of the admixtures were finalized. The Vicat setting time and Compressive Strength test were then conducted on the optimized proportions of admixtures for the verification of the analysis. Analysis was conducted to determine the effect of IPANEX on the setting time and compressive strength and its synergistic effect on the other admixtures.

OPTIMIZATION OF ANTIFREEZE ADMIXTURE FORMULATIONS

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