Durability Increase of Special Concrete by Application of Waste Raw Materials

Transcription

1 10DBMC International Conference On Durability of Building Materials and Components Durability Increase of Special Concrete by Application of Waste Raw Materials R. Drochytka, T. Fojtík Brno University of Technology, Faculty of Civil Engineering Veveří 95, Brno, Czech Republic TT3-200 ABSTRACT A great deal of research is currently focused on the durability of building structures and concrete degradation caused by the effect of corrosive liquids or the gaseous phase. Test results have shown that concrete resistance to aggressive media can be increased by the addition of suitable types of waste materials or admixtures having pozzuolana properties. The paper discusses the potential for increases in durability of special concrete types, including Self Compacting Concrete, High Performance Concrete, Reactive Powder Concrete by addition of suitable waste materials (power plant fly ash) or admixtures (meta-kaolin). The aim of the work is to verify, compare and analyze the effect of addition of power plant fly ash and meta-kaolin respectively to concrete subjected to immersion in aggressive media. Concrete were prepared with and without the utilization of waste raw materials or admixtures. The concrete was stored in different aggressive liquid media (SO 4 2-, Cl, oil) or gases (simulated concentrations of CO 2, SO 2 with different relative humidities, and ambient exterior atmospheric conditions) and reference were stored in water. The storage periods were 3 and 6 months. After storage, specimens were tested by physico-mechanical and physico-chemical methods, and their appearance and state after exposure to individual aggressive effects was recorded. Results from short-term test of 6 months exposure in aggressive media show that enhanced durability can be achieved with concretes incorporating power plant fly ash or meta-kaolin. No significant changes of physico-mechanical and physico-chemical properties were found in any of concrete modified by power plant fly ash or meta-kaolin after 6 months of storage in. Definite conclusions regarding the enhanced performance of these modified concretes cannot be made given that an exposure period of 6 months is too short for generalization of results. However, these initial results can help orient further research and further work continues with additional tests results from exposure periods of 48 months to be reported at a later date. KEYWORDS Waste raw materials, Reactive Powder Concrete, Self Compacting Concrete, High Performance Concrete.

2 1 INTRODUCTION Over the past decades it is apparent that High Strength Concrete (HSC) is increasingly being used and on a continually larger scale given the improved levels of performance. Of basic interest is the characteristic high compressive strength of this concrete that may range from at least 65 N.mm -2 to upwards of 100 N.mm -2. Research in this area is on-going and research results indicate that significantly higher compressive strengths can bee achieved of up to, for example, 200 N.mm -2 and more. Such type of concretes have by some been categorised as Ultra High Strength Concrete (UHSC) and one representative type of UHSC developed in France is RPC (Reactive Powder Concrete). In essence, UHSC is characterised by having extremely high physico-mechanical parameters. Increasingly the current trend is to utilize functional industrial wastes, such as power plant fly ash, in the formulation of concrete mixes. However, the long-term performance of concretes prepared with the addition of different waste raw materials is not readily understood, nor for example, what level of enhanced resistance to deterioration such concretes may offer when exposed to different environmental conditions, in particular, aggressive media and corrosive environments in which concretes are often exposed. 2 METHODS AND TECHNIQUES A study was conducted to verify possible increases in durability (or resistance to deterioration) of new types of concrete such as Reactive Powder Concretes (RPC), Self Compacting Concretes (SCC) and High Performance Concretes (HPC) by the addition of waste materials (e.g. power plant fly ash), or admixtures having pozzuolana properties (e.g. micro-silica). The primary focus of this study was determining the resistance to deterioration when such types of concrete are subjected to an aggressive chemical environment. The study was undertaken in two phases, the first of which was determining the base composition of the different concrete types and the amounts of either fly ash or admixture to be incorporated in the mix in relation to standard concrete, in which no admixtures nor fly ash were added. Various trials and test batches helped establish the final composition of the concrete mixes and were used to adjust mix proportions to achieve the desired functional properties of the different blended concretes. The second phase of work was divided into two parts, the first of which focused on the use of fly ash as an additive to enhance the durability of either RPC or SCC; the second part consisted of incorporating meta kaolin to High Performance Concrete (HPC) as a means to improve durability in this type of concrete. In both parts of the study, concrete, incorporating additives in the concrete mix, were compared to a standard concrete mix in terms of their physico-mechanical properties when subjected to immersion in aggressive media for a period of 3 to 6 months. In this manner, the effect of the additives on the physico-mechanical and physico-chemical properties of the different concrete types could be determined depending on the aggressive medium in which the test pieces were stored. The determined values characterizing the properties and the state of the Comparison in terms of the physico-mechanical and physico-chemical properties of the different concrete types are made between test specimens stored in to those stored in water under standard conditions (state conditions). Likewise, comparisons could be made between the properties of concrete incorporating selected quantities of waste materials or admixtures and a standard concrete mix that does not include waste materials or admixtures. This permits determining the potential for enhanced long-term performance (durability) of these novel concrete mixes. Test specimens for High Performance Concrete (HPC) and Self Compacting Concrete (SCC) were cubes (100-mm) cast in steel moulds. Specimens were demoulded after 24 hours and were cured for 28 days in water following Standard conditions (T = 22 C and RH = 100%). Specimens prepared for the Reactive Powder Concrete (RPC) were cast in the form of prismatic beams having dimensions of 40 by 40 by 160 mm. The test specimens were demoulded 5 to 6 hours after being cast and were cured for a period of 72 ± 2 hours in controlled conditions of 100 % relative humidity and a temperature of 90±3 C. After this period, the RPC test specimens were placed in water as other test pieces.

3 The composition of different types of concrete, including RPC, HPC and SCC, are found in Tables 1, 2 and 3 respectively. Concrete components RPC I RPC II [kg.m -3 ] [kg.m -3 ] Cement-SVC III/A 32,5 R Quartz sand - PR Fly ash - 60 Micro-silica Water Plasticizing admixture Chrysofluid Premia Table 1: Composition of Reactive Powder Concrete (RPC) Concrete components SCC I SCC II [kg.m -3 ] [kg.m -3 ] Cement - CEM I 42,5 R Aggregates 0/4 mm /8 mm /16 mm Fly ash - 90 Plasticizing admixture Chrysufluid Optima 200 7,2 5,76 Water Table 2: Composition of Self Compacting Concrete (SCC) Concrete components HPC I HPC II [kg.m -3 ] [kg.m -3 ] Cement - CEM I 42,5 R Aggregates 0/4 mm /8 mm /16 mm Meta-kaolin - 43 Plasticizing admixture -Woerment FM 794 7,4 7,4 Water Table 3: Composition of High Performance Concrete (HPC) 3 PROGRESS OF EXPERIMENTAL WORK 3.1 Possibility of increase in durability by addition of industrial waste (power plant fly ash) to Reactive Powder Concrete (RPC) and Self Compacting Concrete (SCC) The aim of this part of the paper has been to verify the durability of Reactive Powder Concrete (RPC) and of Self Compacting Concrete (SCC) by application of power plant fly ashes. This concrete was produced both with the addition of definite quantity of admixture and without this admixture. The test pieces produced from this concrete were exposed to selective aggressive media and the reference were stored in water medium following Standard demands. The test pieces were stored in testing media for the period of 3 to 6 month and after this period the test pieces were checked by physico-mechanical tests and by physico-chemical analysis i.e. there were determined the physicomechanical and physico-chemical parameters of, their appearance and state after the effect of

4 individual aggressive medium for the given period. The obtained values were compared on the one hand following the individual aggressive media and on the other hand of course with values obtained with reference test that were stored in Standard atmosphere. More important are naturally the properties and state comparison of the same concrete type produced with and without use of waste raw materials. The possibility of durability increase by application of waste raw materials can be evaluated just by comparison of identical concrete types produced without the use of admixture (meta-kaolin) and with the use of this admixture. 3.2 Possibility of increase in Durability by addition of puzzolona-based admixtures (meta-kaolin) to High Performance Concrete (HPC) The aim of this part of the paper has been to verify the possibility of increases in durability of High Performance Concrete (HPC) by the addition of meta-kaolin to the concrete mix. As is provided in Table 3, concrete mixes were produced with (HPC II) and without (HPC I) the addition of admixture. The test specimens prepared from both these concrete mixes were exposed to chemically aggressive media and the reference were stored in water following standard requirements. The test specimens remained exposed to the aggressive environment for periods of 3 and 6 months after which they were subjected to mechanical tests and physico chemical analysis. Comparisons of results were made, as provided in Figures 6 and 7. The selection of different types of aggressive media was based on ensuring the broadest range of substances to which concrete is typically exposed in an industrial environment. The individual types of selected aggressive media, including their characteristic properties, are provided in Table 4. Characteristic of medium Substance Concentration Relative humidity Gaseous - CO 2 98% 75% Gaseous - SO 2 98% 75% Sulphates - Na 2 SO mg l Chlorides NH 4 Cl mg l Engine oil 100% -- Effect of atmospheric action Outside storage Table 4: Specification of corrosive media Throughout the storage period, the concentration of the different aggressive substances used in the tests was controlled and maintained at constant value. 4 RESULTS 4.1 Reactive Powder Concrete (RPC) The following graphs provide a summary of results from mechanical tests on concrete mixes RPC I and RPC II after 6 months (180 days) of storage under different aggressive conditions. Comparative values between the two types of RPC concrete mixes of compressive and tensile strength and dynamic elastic modulus are given in Figures 1, 2 and 3 respectively. refer to those that were stored in standard conditions and not subjected to any special environmental conditions.

5 154 Compressive strenght [MPa RPC I RPC II Fig. 1: Comparison of compression strength of RPC I and RPC II after 180 days storage in 24 Tensile strenght [MPa 23, , , ,5 20 RPC I RPC II Fig. 2: Comparison of bending strength of RPC I and RPC II after 180 days storage in different aggressive media 50 Dynamic Modulus of Elasticity [GPa] Srovnávací vzorky RPC I RPC II Fig. 3: Comparison of dynamic elasticity modulus of RPC I and RPC II after 180 days storage in

6 4.2 Self Compacting Concrete (SCC) The summary of analysed SCC I and SCC II properties after 6 month of storing under aggressive conditions you will find in following graphs. 50 Compressive strenght [MPa SCC I SCC II Fig. 4: Comparison of compression strength of SCC I and SCC II after 180 days storage in Dynamic Modulus of Elesticity [GP SCC I SCC II Fig. 5: Comparison of dynamic elasticity modulus of SCC I and SCC II after 180 days storage in 4.3 High Performance Concrete (HPC) The summary of analysed HPC I and HPC II properties after 6 month of storing under aggressive conditions you will find in following graphs.

7 84 Compressive strenght [MPa HPC I HPC II Fig. 6: Comparison of compression strength of HPC I and HPC II after 180 days storage in Dynamic Modulus of Elasticity [GP HPC I HPC II Fig. 7: Comparison of dynamic elasticity modulus of HPC I and HPC II after 180 days storage in 5 CONCLUSIONS Concrete modified by the addition of waste raw material (power plant fly ash) and by admixtures having properties similar to pozzuolana attained comparable physico-mechanical properties as those of standard PC concrete. Specifically, the following was noted: - Reactive Powder Concrete (RPC) modified by fly ash (5 % of filler mass) had moderate increases in flexural and compressive strength ;values of dynamic modulus of elasticity were approximately the same. - Self Compacting Concrete (SCC) modified by power plant fly ash (20% of cement mass) had lower values of compressive strength than concrete without modification. This was caused

8 by the higher water/cement ratio necessary to achieve the same consistency of analysed concrete and mainly due to the effect of a slower rate of reaction from fly ash pozzuolana. - Replacement of 10 % of cement mass by meta-kaolin in HPC has no significant effect on the quality of HPC; the values of compressive strength and dynamic elasticity modulus are nearly identical. The effect of waste raw materials (admixtures) on the durability of concrete was evaluated in phase II of study. No significant changes in concrete properties (e.g. compressive and flexural strength, dynamic modulus of elasticity) have taken place after 6 months of storage in selected aggressive chemical media. As well, the appearance and mass of test specimens did not change. This was supported by a study of the phase composition using X-ray analysis reported elsewhere. In regard to the partial substitution of binder (filler) for power plant fly ash or meta-kaolin (HCP) in the concretes evaluated in this study (i.e. RPC, SCC), it can be stated that the substitution has not caused more significant change in concrete properties as compared to standard concrete not even during an exposure period of 6 months in aggressive media. However, it is generally known that the effect of aggressive chemicals on concrete usually bring about changes after longer periods of exposure and therefore these effects will be subsequently reviewed after 48 months of exposure to aggressive chemical media. 6 ACKNOWLEDGMENTS The paper was prepared with the support of the Czech funded scientific research project CEZ MSM , entitled: Research and Development of New Materials from Waste Raw Materials to Secure Greater Durability in Building Structures and with the support of the Brno University of Technology Development Fund No. 1742, entitled: Durability Increase of Building Materials by Application of Wastes 7 REFERENCES Matoušek, M., Drochytka, R.: Atmospheric Corrosion of Concrete, IKAS Praha 1998 (in Czech) Drochytka, R.: Atmospheric Corrosion of Concrete and Cellular Concrete. Sborník vědecké konference VUT FAST Brno, 1984, sv. B-97, pp (Proceedings of Konference at Brno University of Technology (in Czech)