OPTIMIZATION OF PRESSURE AND CURING TIME IN PRODUCING AUTOCLAVED AERATED CONCRETE

Transcription

1 Proceeding the 6th Civil Engineering Conference in Asia Region: Embracing the Future through Sustainability ISBN OPTIMIZATION OF PRESSURE AND CURING TIME IN PRODUCING AUTOCLAVED AERATED CONCRETE Januarti Jaya Ekaputri, Triwulan 2, Dody Brahmantyo 3, and Farid Raja Sultan Nasir 4 ITS, Kampus ITS Sukolilo Surabaya 6, januarti_je@yahoo.com 2 ITS, Kampus ITS Sukolilo Surabaya 6, triwulan_marwan@yahoo.com 3 Universitas Narotama, Jl. Arief Rahman Hakim 5 Surabaya 67, dodybrahmantyo@yahoo.co.id 4 ITS, Kampus ITS Sukolilo Surabaya 6, fadhliirobbii@gmail.com ABSTRACT Most autoclaved aerated concrete (AAC) is produced from materials such as quartz sand, lime, Portland cement and other constituent categorized as pozzolanic materials. The density of the concrete is less than kg/m 3. Using less Portland cement and being easy to be formed are the advantages of applying AAC as bricks at the construction site. In this paper, the material to produce AAC were composed of Portland cement, calcined Sidoarjo volcano-mud, lime, sand and Aluminum powder as foaming agent. Specimens were cured in autoclaved at varied pressures at a different period of time to obtain an optimum curing system. The results showed that the autoclaving system using pressure of 4 bars for six hours were recommended for the curing system. The averages of compressive strength of specimens at 7days were 2.4 MPa with the density of 87 kg/m 3. Longer curing system resulted in lower compressive strength. INTRODUCTION Concrete is widely used in construction industry because it s compressive strength. Concrete is also easily molded as desired. However, the weight itself is relatively great, so that when a building is attacked by an earthquake, the earthquake forces will be amplified because the force is proportional to the weight of the building. It means that the weight of the building contributes the earthquake force. Because of these reasons, the current developing of concrete material technology is creating buildings with a strong concrete based material but reducing the weight of non-structural elements by applied lightweight concrete. Wall system is one of the nonstructural members which can be made from lightweight concrete. By using less volume of cement, a lightweight concrete was made from silica fume, perlite, fly ash, quartz sand, lime, gypsum and other materials that are categorized as materials for lightweight concrete (Karakurt et al, 2). It is not only having density less than g/cm 3, but conveniently formed and mobilized during construction. They are one of the advantages of lightweight concrete compared with normal concrete. In the manufacturing process, lightweight concrete is cured in a steam pressure system for 2 hours at a high temperature at around 9 C and the steam pressures up to 2 bars or 2 MPa (Matsui et al, 2). Sidoarjo Mud (Lusi) is a material having potential to reduce cement content in making lightweight concrete. The activated siliceous mud can be applied as cement substitution. It has also substantial fine particles but high shrinkage so that the mud is usually incorporated with additional materials such as fly ash or silica sand to increase the compressive strength and its stability. To activate the oxide content, the mud is calcined at a certain temperature. The optimum calcination temperature usually is kept constant at 6 C -8 C for at least two hours (Hardjito et al, 22). Aluminum powder is generally applied in making lightweight concrete to accelerate the foaming process to reduce the density of concrete (Aroni & Wittman, 992). This process causes a chemical reaction which releases gas. After the mixture hardens, porous concrete is formed (Scheffler & Colombo, 25). Usually, after setting the lightweight concrete were cured in an autoclave at a temperature of 2-25 C and a pressure of 5-2 bars for 8-2 hours. Autoclaving significantly increases the compressive strength due to its high temperature and pressure to produce a stable form of voids. Final strength obtained depends on the pressure and duration of autoclaving process. The process increases the strength and reduces the density of lightweight concrete (Topcu & Uygunoglu, 27).

2 This study investigated the effect of pressure and autoclaved curing time on the mechanical properties of autoclaved aerated concrete made with Sidoarjo mud. The effect of lime addition to the mixture was also studied. MATERIALS An Ordinary Portland Cement (OPC) having specific gravity of 3. g/cm 3 was used to mix with Sidoarjo mud with specific gravity of 2.6 g/cm 3. The mud was prepared with a particle size up to 75 mm (sieve number 2). A lime containing 98% of hydrated lime was added to accelerate the hydration process. The specific gravity of the lime is 2.3 g/cm 3. The aluminum powder was applied as a foaming agent. Chemical composition of material is listed in Table. The mineral content in Sidoarjo mud is shown in Fig.. Tab. : Chemical composition by XRF method (%) Materials CaO Fe 2 O 3 SiO 2 Al 2 O 3 SO 3 K 2 O MnO LOI OPC Calcined mud (hydrated) Fig. : XRD analysis of Sidoarjo mud calcined at 8 o C TS4C-5

3 Compressive Strength (MPa) Compositions The composition of the proposed lightweight concrete is presented in Table 2. The aluminum powder as foaming agent for all mixture was % by cement weight. Specimen code (Px- ) Tab. 2: Composition of lightweight concrete Materials (% from total binder) OPC Calcined Mud Water Aluminum Powder (%) from cement weight P P P- 8 6 Note: x is lime content. For example, P- contains % of lime by binder weight and % of aluminum by cement weight METHODS Three identical cubical specimens size of 5x5x5 cm 3 from each variation were cast and settled for 24 hours before remolding. Specimens were leveled and settled into a vacuum machine for -5 minutes to reduce the moisture remaining in the pores of concrete. Specimens were cured in an autoclave with a certain pressure. Steam pressures from the autoclave were applied ranging from 5, 9, and 4 bars, while the length of the treatment process ranging from 2, 3, 4, 6, 8, and hours. Compression test and density of light weight concrete were analyzed at the age of seven days. The results were compared with the non-autoclaved specimens curing at room temperature for 4, 28 and 56 days. Variations in pressure and length of treatment will be recommended in this paper. RESULTS AND DISCUSSIONS The Effect of Pressures and Content. Fig.2 illustrates the relationship between the addition of lime to the compressive strength. Specimens were cured in the autoclave at a pressure of 5, 9 and 4 bar for four hours. In the picture, it is shown that the addition of lime decreases the compressive strength. Specimen P- which containing % of lime showed the highest strength compared with other specimens. When the specimens were cured with steam pressure at 4 bars, the strength increased. The highest strength was also provided by specimens P-. As well known, an excessive lime added to the mixture of cement paste decrease the strength. However, by performing about 5-2 bars the autoclave treatment increases the compressive strength of bricks made from lime (Cicek & Tanriverdi, 27). Usually the optimum content of lime in the production of lightweight concrete ranges from % to 5% by weight of binder.,5,5 4 Bars 9 Bars 5 Bars % 5% 2% Fig. 2: The effect of lime content on the compressive strength of specimens in different pressure steam TS4C-52

4 Compressive Strength (MPa) Compression Strength (MPa) The Effect of Curing Duration. The relationships between curing duration with the compressive strength specimens is presented in Fig. 3(a). The specimens were cured at the same steam pressure of 4 bars for two, three and four hours. Specimens cured with the autoclave for four hours produced the best performance. This is according to research conducted by Zhao (22). Increasing the duration of autoclaving produces higher compressive strength. The longer curing time will improve the mechanical properties of lightweight concrete. For example, as illustrated in Fig. 3(b), compressive strength of.6 MPa is shown by specimen P- cured at two hours. When the autoclaving duration was prolonged to three hours then the strength increased to.7 MPa. When the time was extended to four hours, the strength increased to.3 MPa. The effect of curing duration showed more effect on the compressive strength than the effect of lime content.,5,3 MPa,5,3,5 4 hours 3 hours 2 hours,5,6,7, P- P5- % 5% 2% P2- Curing Duration (hours) (a) Fig. 3: Effect of the curing time on the compressive strength It is known that calcium silicate hydration changes into solution. When the curing time is prolonged, this solution freely moves between hydration products leads to diffusion in solution between the particles. Formation of hydration product increases since the crystalline in layers between the particles also increases. This process will generate strength of lightweight concrete. The test results were also consistent with research conducted by Hanecka (997). Autoclaving significantly increases the compressive strength due to high temperature. The pressure generated stable voids. The strength is obtained mainly depends in pressure and expected duration of autoclaving. Comparison with Non-Autovlaved Specimens. Non-autoclaved specimens were compressed at the age of 4, 28 and 56 days. The strength of specimens increased since the hydration reaction slowly takes place. Under room curing condition, quartz filler is less reactive. Fig.4 shows that the specimen P- (56) has the highest strength of.4 MPa at the age of 56 days while the specimen P2- (4) has the lowest strength of. MPa at 4 days. The results were then compared with the autoclaved-specimens. This proves that the pressure system at 4 bars is required in the process of lightweight concrete. The strength increased as the pressure of steam was increased. It is illustrated in Fig. 5 that steam pressure at the higher temperature (approximately 8 o C at 4 bars) initiates the increase of concrete strength. It might be due to the reaction of quartz with cement paste. Yazici et al (23) reported that quartz source under autoclaving generated a formation of tobermorite. Tobermorite belongs to a wider family of cement minerals that contributes higher mechanical performance. It appears when the steam pressure reaches bars, the non-autoclaved curing system remains a non-reacted silica source in the mixture. Thus, it indicates that the requirement of steam pressure curing plays an important role in the factor improving the compressive strength. (b) TS4C-53

5 Density (g/cm 3 ) Compressive Strength (MPa) Compressive Strength (MPa),4,3,2, P- P5- P Age (days) Fig. 4: Compressive strength of non-autoclaved specimens,4,2,8,6,4,2 % 5% 2% 9 Bars-4h 56 days 28 days 4 days 4 Bars-4h Fig. 5: Strength comparison of non-autoclaved and autoclaved specimens Fig. 6 shows the temperature of curing influence the density of lightweight concrete. Because of drying shrinkage occurred, density of non-autoclave specimens decreased. Specimens containing more lime showed less density than others due to lower specific gravity of lime. As the temperature was increased during autoclaving, crystallization occurred in autoclaved-specimens. This process decreases drying shrinkage and increases denser pores with stable void shape. It can be explained that the density of autoclaved-specimen is slightly higher than the density of the non-autoclaved specimens.,9,8,7,6 % 5% 2% 4 Bars-4h 9 Bars-4h 56 days 28 days 4 days Fig. 6: Density comparison of non-autoclaved and autoclaved specimens TS4C-54

6 Density (g/cm 3 ) Compressive Strength (MPa) Relation between Curing Time and Compressive Strength. It has been determined that by providing a certain steam pressure in the autoclave curing will produce a higher compressive strength. Further optimization of curing duration was obtained by using only pressure that produced the highest mechanical property. Steam pressure was kept constant at 4 bars with different treatment times ranging from 2, 4, 6, 8 and hours. Fig. 7 shows a relation between curing duration and compressive strength. The highest strength of 2.4 MPa is shown by specimen P- cured for six hours. The increased compressive strength under steam pressure is probably contributed by the effect pozzolanic reaction and the hydration of cement. However, extended autoclaving period may cause the strength decrease. The optimum compressive strength can be achieved in a shorter curing duration at higher temperatures to generate the hydration of calcium silicates and pozzolanic activity (Kearsley and Booysens, 998). It is believed that longer exposure steam pressure causes the formation of excessive crystalline calcium silicate. It will induce the strength reduction. 2,5 2,4 2,5,5 2,2, Curing Duration (hours) P-(4,t) P5-(4,t) P2-(4,t) Fig. 7: Effect of autoclave duration at pressure of 4 bars on the compressive strength Density of Autoclaved-Specimens. Relation between strength and density is presented in Fig. 8. All specimens were cured at steam pressure of 4 bars. The data was taken at seven days after casting. As expected, the strength was the function of density. The strength improves with the increase of density. Denser and stable pore shape generated the increase of strength. The density of specimens with minimum strength of 2 MPa was.82 g/cm 3.,85,8,75,7 R² =,9,65,6,5,5 2 2,5 Compressive Strength (MPa) Fig. 8: Compressive strength and density relation TS4C-55

7 CONCLUSIONS content reduced the density of lightweight concrete, but in excessive usage, it induced to decrease the strength. It is certainly recommended that the optimum lime content in the mixture is -5% by binder weight. The length of standard curing in room temperature can be achieved in a very short period by autoclave curing. However, prolonged exposure curing will influence the strength. In this study, the optimum curing period is six hours with steam pressure at 4 bars. It was revealed that the density was the function of compressive strength. REFERENCES Karakurt, C., Kurama, H. and Topcu, I.B. (2). Utilization of Natural Zeolite in Aerated Concrete Production. Cement & Concrete Composites, 32, -8. Matsui, K., Kikuma, J., Tsunashima, M., Ishikawa, T., Matsuno, S., Ogawa, A. and Sato, M. (2). In Situ Time-Resolved X-Ray Diffraction of Tobermorite Formation in Autoclaved Aerated Concrete- Influence of Silica Source Reactivity and Al Addition. Cement & Concrete Research, 4, Hardjito, D., Antoni, Wibowo, G.M. and Christianto, D. (22). Pozzolanic Activity Assessment of LUSI (LUmpur SIdoarjo) Mud in Semi High Volume Pozzolanic Mortar. Materials, 5, Aroni, S. and Wittman, F.H. (992). Autoclaved Aerated Concrete, Properties Testing and Design. RILEM Technical Commites, 78 MCA and 5 ALC. Scheffler, M. and Colombo, P. (25). Cellular Ceramics: Structure, Manufacturing, Propertiesand Applications, Cellular Concrete. Willey-VCH Verlag & Co. Pensylvania, USA. Topcu, I.B. and Uygunoglu, T. (27). Properties of Autoclaved Lightweight Aggregate Concrete. Building and Environment, 42, Cicek, Y. and Tanriverdi, M. (27). Based Steam Autoclaved Fly Ash Bricks. Construction and Building Materials, 2, Zhao, Y., Zhang, Y., Chen, T., Chen, Y. and Bao, S. (22), Preparation of High Strength Autoclaved Bricks from Hematite Tailings. Construction and Building Materials, 28, Hanecka, C., Koronthalyova O. and Matiasovsky, P. (997). The Carbonation of Autoclaved Aerated Concrete. Cement and Concrete Research, 27, Yazici, H., Deniz, E. and Baradan, B. (23). The Effect of Autoclave Pressure, Temperature and Duration Time on Mechanical Properties of Reactive Powder Concrete. Construction and Building Materials 42,, Kearsley, E.P. and Booysens, P.J. (998). Reinforced Foamed Concrete-Can it be Durable?. Foamed Concrete, 9, 5-9. TS4C-56