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Use of GGBS Concrete Mixes for Aggressive Infrastructural Applications

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Use of GGBS Concrete Mixes for Aggressive Infrastructural Applications UCD School of Architecture, Landscape and Civil Engineering Use of GGBS Concrete Mixes for Aggressive Infrastructural Applications ENTERPRISE IRELAND ECOCEM IRELAND INNOVATION PARTNERSHIP PROGRAMME PROJECT CODE IP/2008/0540 Executive summary The case for research into the deterioration associated with water and wastewater infrastructure has been clearly made. For example in the US alone, the Congressional Budget Office has estimated that annual investments of up to $20 billion and $21 billion is required to provide adequate infrastructure for drinking water and wastewater respectively. It is also estimated that the annual operation and maintenance costs associated with drinking water and wastewater infrastructure to be in excess of $31 billion and $25 billion respectively. In Ireland, the Government have previously announced that under the Water Services Investment Plan, €5.8 billion will be spent on this sector. As such, this represents a potentially lucrative market that exists both in Ireland and internationally. Research was conducted into the performance of concrete samples manufactured using a range of binder combinations which were subjected to aggressive environments selected to represent the most extreme of conditions they will encounter in service. These included attack from sulfates and from biogenic sulfuric acid. The test results found that: • In sodium sulfate expansion tests, traditional CEM I cements performed significantly poorer than all other binder combinations. Samples manufactured using the newer CEM II/A-L binders displayed increased resistance to sulfate attack but still failed to meet standard performance criteria. • The samples with the highest resistance to sulfate attack were those that contained 50% or 70% GGSB as a cement replacement level, which displayed very low expansion levels. This also included superior resistance levels than that obtained using sulfate-resisting Portland cement. • In all cases deterioration was primarily due to bulging, spalling and warping, most likely as a result of the formation of gypsum. • When subjected to a 1% sulfuric acid solution (pH 1.3), significant surface corrosion was observed for all binder combinations. Very little distinction was observed between the various binder combinations. • The main deterioration mechanism consisted of the formation of gypsum on the external surfaces of the concrete specimens. This was followed by surface delamination, some spalling. In the long term a widespread lack of cohesion leads to a failure mechanism that spreads directly to the core. The results of this investigation have clearly outlined the cause of concrete deterioration in wastewater treatment systems and distinguished between degradation due to sulfate attack and that due to a sulfuric acid attack in this environment. There is a need to train concrete specifiers in understanding the harsh conditions that these structures will encounter in service. However for this to be fully realised, the range of aggressive environments associated with wastewater applications needs quantification. Dr Ciaran McNally, Project Manager TABLE OF CONTENTS 1 INTRODUCTION .................................................................................................................... 1 2 LITERATURE REVIEW ......................................................................................................... 3 3 EXPERIMENTAL PROGRAMME: MATERIALS AND METHODS ................................. 4 3.1 Experimental Overview .................................................................................................... 4 3.2 Materials and methods ...................................................................................................... 5 3.2.1 Sodium sulfate expansion tests .................................................................................. 5 3.2.2 Sulfuric acid tests ....................................................................................................... 7 3.3 Ultrasonic Tests .............................................................................................................. 10 3.3.1 Review of current research ....................................................................................... 10 3.3.2 Experimental setup ................................................................................................... 11 3.4 Permeability tests ............................................................................................................ 13 4 EXPERIMENTAL PROGRAMME: RESULTS ................................................................... 14 4.1 Overview ........................................................................................................................ 14 4.2 Sodium sulfate expansion results ................................................................................... 14 4.3 Discussion of sodium sulfate expansion results ............................................................. 23 4.3.1 Dilution effect .......................................................................................................... 23 4.3.2 Permeability and porosity ......................................................................................... 24 4.3.3 The Influence of C 3A ............................................................................................... 25 4.3.4 Influence of C 3S and C 2S ......................................................................................... 27 4.3.5 Sulfate resisting capabilities of CEM II/A-L and GGBS concretes ......................... 27 4.4 Sulfuric acid test results .................................................................................................. 29 4.4.1 Mass loss results ....................................................................................................... 29 4.4.2 Discussion of deterioration mechanism ................................................................... 34 4.4.3 Cube strength tests ................................................................................................... 36 4.4.4 Sulfuric acid expansion tests .................................................................................... 37 4.5 Ultrasonic results ............................................................................................................ 38 4.5.1 Stiffness loss in due to sulfuric acid testing ............................................................. 38 4.5.2 Stiffness loss in concrete exposed to a 1% sulfuric acid solution ............................ 41 4.5.3 Discussion of ultrasonic results ................................................................................ 46 4.5.4 Microstructural Effects ............................................................................................. 46 4.5.5 Chemical effects ....................................................................................................... 48 4.6 Permeability, absorption and sorptivity results .............................................................. 49 5 DISCUSSION ........................................................................................................................ 51 5.1 Sulfate experimental programme.................................................................................... 51 5.2 Sulfuric acid programme ................................................................................................ 52 5.3 Ultrasonic analysis .......................................................................................................... 54 6 CONCLUSIONS .................................................................................................................... 56 6.1 Sodium sulfate tests ........................................................................................................ 56 6.2 Sulfuric acid tests............................................................................................................ 57 6.3 Summary ......................................................................................................................... 58 1 INTRODUCTION The deterioration of wastewater infrastructure has long been a cause for concern but the issues surrounding the problem remained unknown for many years. Traditionally designed to resist high levels of sulfate attack, wastewater treatment systems are subjected to a considerably more aggressive form of deterioration – biogenic sulfuric acid corrosion. To this day the true mechanisms of attack have yet to be fully grasped by concrete specifiers and this is evident in the poor state of infrastructure used in this environment. There is clearly a need to distinguish between the two forms of attack and the research conducted in this investigation shows that both the nature and severity of attack is drastically different. Existing methods aimed at counteracting the corrosive forces focus on remedial work, periodic maintenance and replacement of defective components. This is clearly not a cost effective practice especially considering that this form of attack can manifest itself within a relatively short period of time (under ten years). In examining current European standards one discovers it is not necessarily the fault of the specifier that integrity of wastewater infrastructure is being compromised at such an early age, but rather a combination of a lack of understanding of the true mechanisms at work (owing to largely disjointed research efforts) and a concrete standard that does not adequately
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