Structural lightweight aerated concrete By Algurnon Steve van Rooyen Thesis presented in fulfilment of the requirements for the degree Master of Science in Engineering in the Faculty of Engineering at Stellenbosch University Supervisor: Prof GPAG van Zijl March 2013 Stellenbosch Univeristy http://scholar.sun.ac.za DECLARATION I, the undersigned, hereby declare the work contained in this thesis is my own original work except where specifically referenced in text, and that I have not previously in its entirety or in part submitted it at any university for a degree. Date :…………………………………………… Signature :…………………………………………… (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:3) (cid:38)(cid:82)(cid:83)(cid:92)(cid:85)(cid:76)(cid:74)(cid:75)(cid:87)(cid:3)(cid:139)(cid:3)(cid:54)(cid:87)(cid:72)(cid:79)(cid:79)(cid:72)(cid:81)(cid:69)(cid:82)(cid:86)(cid:70)(cid:75)(cid:3)(cid:56)(cid:81)(cid:76)(cid:89)(cid:72)(cid:85)(cid:86)(cid:76)(cid:87)(cid:92) (cid:36)(cid:79)(cid:79)(cid:3)(cid:85)(cid:76)(cid:74)(cid:75)(cid:87)(cid:86)(cid:3)(cid:85)(cid:72)(cid:86)(cid:72)(cid:85)(cid:89)(cid:72)(cid:71)(cid:3) AS VAN ROOYEN | PREFACE i Stellenbosch Univeristy http://scholar.sun.ac.za SYNOPSIS Cellular concrete is a type of lightweight concrete that consists only of cement, water and sand with 20 per cent air by volume or more air entrained into the concrete. The two methods used for air entrainment in cellular concrete are (1) the use of an air entraining agent (AEA), and (2) the use of pre-formed foam. If pre-formed foam is used to entrain air into the concrete the concrete is named foamed concrete and if an AEA is used the concrete is termed aerated concrete. Depending on the type of application, structural or non- structural, cellular concrete can be designed to have a density in the range of range of 400 to 1800 kg/m3. Non-structural applications of cellular concrete include void and trench filling, thermal and acoustic insulation. Structural applications of cellular concrete include pre-cast units such as concrete bricks, partitions, roof slabs etc. Due to the high levels of air in cellular concrete it is challenging to produce compressive strengths that are sufficient to classify the concrete as structurally useful when non-autoclaving curing conditions are used. The autoclaving process combines high temperature and pressure in the forming process, which causes higher strength and reduced shrinkage. This process is also limited to prefabricated units. Non-autoclave curing conditions include moist curing, dry curing, wrapping the concrete in plastic, etc. However, now that the world is moving in an energy efficient direction, ways to exclude energy-intensive autoclaving are sought. It has for instance been found that the utilisation of high volumes of fly-ash in cellular concrete leads to higher strengths which make it possible to classify the concrete as structurally useful. Now, that there is renewed interest in the structural applications of the concrete a design methodology using an arbitrary air entraining agent needs to be found. The research reported in this thesis therefore attempts to find such a methodology and to produce aerated concrete with a given density and strength that can be classified as structurally useful. For the mix design methodology, the following factors are investigated: water demand of the mix, water demand of the mix constituents, and the amount of AEA needed to produce aerated concrete with a certain density. The water demand of the mix depends on the mix constituents and therefore a method is proposed to calculate the water demand of the mix constituents based on the ASTM flow turn table. Due to the complex nature of air entrainment in concrete, the amount of air entrained into the concrete mix is not known beforehand, and a trial and error method therefore had to be developed. The trial mixes were conducted in a small bakery mixer. From the trial mixes estimated dosages of AEA were found and concrete mixes were designed based on these mixes. AS VAN ROOYEN | PREFACE ii Stellenbosch Univeristy http://scholar.sun.ac.za The factors that influence the mix design and strength of aerated concrete include filler/cement ratio (f/c), fly-ash/cement ratio (a/c) and design target density. Additional factors that influence the strength of aerated concrete are specimen size and shape, curing, and concrete age. It was found that the sand type and f/c ratio influence the water demand of the concrete mix. Sand type and f/c ratio also influence compressive strength, with higher strength for a finer sand type and lower f/c ratios. However, the concrete density is the factor that influences the strength the most. AS VAN ROOYEN | PREFACE iii Stellenbosch Univeristy http://scholar.sun.ac.za ACKNOWLEDGEMENTS I would like to thank my mentor and supervisor Prof. Gideon P.A.G van Zijl. His guidance and motivation has been a source of tremendous help and source of comfort. I also thank my mother (Astrid van Rooyen) and my sister (Nicole Fortune) for being there for me through thick and thin, even at times when contact was minimal. They are my rock. I thank the staff of the structural engineering division. I thank my friends for their support, especially Ms E Davis for everything. Most of all I thank God for giving me the ability to understand and comprehend. He has lead me through tough times throughout my life and everything that I have and will achieve I attribute to Him. I would also like to thank the NRF for their support. The sponsorship of materials by Mapei SA and PPC Cement is gratefully acknowledged. The research was performed under the THRIP project ACM, with industry partners AfriTechnologies, Arup, Aurecon, BKS, Cement and Concrete Institute, Element, Grinaker- LTA and Stefanutti Stocks. Stellenbosch University, through its Overarching Strategic Plan, also supported this work. AS VAN ROOYEN | PREFACE iv Stellenbosch Univeristy http://scholar.sun.ac.za DEFINITION OF TERMS AND ACRONYMS Cellular concrete The term used to collectively describe aerated concrete and foamed concrete Foamed concrete Cellular concrete produced from pre-formed foam Aerated concrete Cellular concrete produced from an air-entraining agent Foaming agent A concrete admixture that is used to entrain air into the concrete either by adding the agent to the concrete mix or by adding the agent to a solution that can produce foam to be added to the concrete base mix. Typical foaming agents are manufactured from hydrolised proteins, vinsol resin, etc. Air-entraining agent A concrete admixture that is classified in the group of air-entraining agents in concrete engineering Lightweight Concrete having a closed structure and a density if not more than aggregate concrete 2200 kg/m3 consisting of or containing a proportion of artificial or natural lightweight aggregates having a particle density less than 2000 kg/m3 (BS EN 1992-1-1:2004, 185) Structural lightweight Aerated concrete having sufficient compressive strength, say 25 aerated concrete MPa or more, to be classified as structurally useful AS VAN ROOYEN | PREFACE v Stellenbosch Univeristy http://scholar.sun.ac.za LIST OF SYMBOLS ρ the target density in kg/m3 m ρ dry density in kg/m3 dry ρ measured density in kg/m3 measured x cement content in kg/m3 c (f/c) filler/cement ratio (w/s*) water/solids ratio (w/s) water/sand ratio (w/c) water/cement ratio (w/a) water/ash ratio (s/c) sand/cement ratio (a/c) fly-ash/cement ratio RD relative density of cement c RD relative density of sand s RD relative density of fly-ash a RD relative density of foam f RD relative density of air entraining agent AEA m mass of the water in kg w m mass of the sand in kg s m mass of the fly-ash in kg a m mass of the air-entraining agent in kg AEA m sum of the masses of the mix constituents in kg tot V volume of the water in litres w V volume of the sand in litres s V volume of the fly-ash in litres a V volume of the air-entraining agent in litres AEA V sum of the volumes of the mix constituents in litres tot V required volume of air to be entrained in the concrete base mix in litres a(req) V volume of foam in litres f σ compressive strength of the concrete in MPa comp σ tensile splitting strength of the concrete in MPa split E modulus of elasticity of the concrete in GPa c σ the compressive stress corresponding to 40 % ultimate load in MPa 1 σ the compressive stress corresponding to 0.005 % strain in MPa 0 ε strain corresponding to the compressive stress at 40 % ultimate load (mm/mm) 1 ε 0.005 % (mm/mm) 0 AS VAN ROOYEN | PREFACE vi Stellenbosch Univeristy http://scholar.sun.ac.za LIST OF TABLES Table 1: Representation of the mix design equations .......................................................... 24 Table 2: Mix composition of Experiment 1 ........................................................................... 40 Table 3: Mix compositions for Experiment 2 ........................................................................ 42 Table 4: Water/sand ratio of the different fillers used........................................................... 45 Table 5: Results of the w/s* and the w/c.............................................................................. 46 Table 6: Compressive strength of the concrete at 7 and 28 days ........................................ 50 Table 7: Results of the tensile splitting strength test in MPa ................................................ 51 Table 8: Results of the elastic modulus test in GPa ............................................................ 52 Table 9: Coefficients and exponents relating the density of the concrete to the compressive strength (Malmesbury sand) ................................................................................................ 57 Table 10: Coefficients and exponents relating the density of the concrete to the compressive strength (Phillippi sand) ....................................................................................................... 57 Table 11: Coefficients and exponents relating the density of the concrete to the tensile splitting strength (Malmesbury sand) ................................................................................... 59 Table 12: Coefficients and exponents relating the density of the concrete to the tensile splitting strength (Phillippi sand) .......................................................................................... 59 Table 13: Results of the concrete compressive strength test using Malmesbury sand as filler ........................................................................................................................................... 66 Table 14: Results of the concrete compressive strength test using Phillippi sand as filler ... 67 Table 15: Results of the concrete tensile splitting strength test using Malmesbury sand as a filler ..................................................................................................................................... 68 Table 16: Results of the concrete tensile splitting strength test using Phillippi sand as a filler ........................................................................................................................................... 68 Table 17: Results of the modulus of elasticity for the different concrete mixes using Malmesbury as filler ............................................................................................................ 69 Table 18: Results of the modulus of elasticity for the different concrete mixes using Phillippi sand as filler ........................................................................................................................ 70 Table 19: Normalised compressive strength of the concrete mixes using Malmesbury sand as filler ................................................................................................................................ 76 Table 20: Normalised compressive strength of the concrete mixes using Phillippi sand as filler ..................................................................................................................................... 76 AS VAN ROOYEN | PREFACE vii Stellenbosch Univeristy http://scholar.sun.ac.za TABLE OF FIGURES Figure 1: The basic chemical nature of surfactants (Myers, 1992)......................................... 6 Figure 2: Distribution of surfactant molecules at the air-water interface (Du and Folliard, 2005) .................................................................................................................................... 7 Figure 3: Interaction between air bubbles and cement particles (Du and Folliard, 2005) ....... 9 Figure 4: Particle distribution of the two fillers used ............................................................. 19 Figure 5: Flow table test for hydraulic cements ................................................................... 20 Figure 6: Series of pictures illustrating the influence the water has on filler ......................... 22 Figure 7: Bakery mixer and Pan mixer ................................................................................ 26 Figure 8: Diagrammatic representation of experiment 1: the role of filler in cellular concrete ........................................................................................................................................... 32 Figure 9: Contest compressive strength testing machine with cubical specimen ................. 36 Figure 10: Tensile splitting test ............................................................................................ 37 Figure 11: Modulus of elasticity test setup with cylindrical specimen ................................... 39 Figure 12: Flow diagram of the factors influencing the strength of concrete ........................ 41 Figure 13: Water demand of the mix constituents ............................................................... 47 Figure 14: Compressive strength at 7 days for f/c = 1.25 .................................................... 48 Figure 15: Compressive strength at 28 days for f/c = 1.25 .................................................. 49 Figure 16: Compressive strength at 7 days for f/c = 1.5 ...................................................... 49 Figure 17: Compressive strength at 28 days for f/c = 1.5 .................................................... 50 Figure 18: Density versus compressive strength (Malmesbury sand - 28 days) .................. 54 Figure 19: Density versus compressive strength (Phillippi sand - 28 days) ......................... 54 Figure 20: Density versus compressive strength (Malmesbury sand - 21 days) .................. 55 Figure 21: Density versus compressive strength (Phillippi sand - 21 days) ......................... 55 Figure 22: Tensile splitting strength versus density (Malmesbury sand) .............................. 58 Figure 23: Tensile splitting strength versus density (Phillippi sand) ..................................... 58 Figure 24: Elastic Modulus versus density (M) .................................................................... 60 Figure 25: Elastic modulus versus density (P) ..................................................................... 61 Figure 26: Concrete compressive strength over time for concrete target density of 2000 kg/m3. Illustrating the influence of the filler on the compressive strength of the concrete ..... 62 Figure 27: Concrete compressive strength over time for concrete target density of 1800 kg/m3. Illustrating the influence of the filler on the compressive strength of the concrete ..... 64 Figure 28: Concrete compressive strength over time for concrete target density of 1600 kg/m3. Illustrating the influence of the filler on the compressive strength of the concrete ..... 65 Figure 29: Compressive strength versus concrete age (Malmesbury sand) ........................ 71 Figure 30: Compressive strength versus concrete age (Phillippi sand) ............................... 72 AS VAN ROOYEN | PREFACE viii Stellenbosch Univeristy http://scholar.sun.ac.za Figure 31: Concrete compressive strength over time for concrete target density of 2000 kg/m3. Illustrating the influence of the filler on the compressive strength of the concrete (Normalized) ....................................................................................................................... 73 Figure 32: Concrete compressive strength over time for concrete target density of 1800 kg/m3. Illustrating the influence of the filler on the compressive strength of the concrete (Normalized) ....................................................................................................................... 74 Figure 33: Concrete compressive strength over time for concrete target density of 1600 kg/m3. Illustrating the influence of the filler on the compressive strength of the concrete (Normalized) ....................................................................................................................... 75 Figure 34: ASTM flow turn table illustrating the spreadability of two concrete base mixes. The concrete base mix on the left has a good consistency. The concrete base mix on the right is too flowable ............................................................................................................. 88 AS VAN ROOYEN | PREFACE ix