Cost analysis of green concrete

Transcription

1 Chapter 6 Cost analysis of green concrete 6.1 INTRODUCTION This chapter gives the most important factor that determines the use of materials in construction. Next to the engineering evaluation of the material, the practical application in construction is the cost of the materials and the degree of work involved. The cost analysis of the two concrete mixtures with the replacements of cement with fly ash and fine aggregate with bottom ash for the binder content of 333 kg/m 3 ; and fly ash for cement, bottom ash for fine aggregate and fly ash aggregate for coarse aggregate replacements with the binder content of 389 kg/m 3, were evaluated, based on their maximum percentage of replacement and compressive strength. 6.2 COST EFFECTIVENESS IN CONCRETE The engineering evaluation, such as strength and durability plays the primary role next to the cost of the construction materials for the designer and for the user. With the help of the pertinent studies, for evaluating the cost effectiveness in concrete, a cost analysis was performed between normal and green concrete with fly ash, bottom ash and fly ash aggregate. 6.3 COST ANALYSIS OF GREEN CONCRETE WITH FLY ASH AND BOTTOM ASH WITH THE BINDER CONTENT OF 333 kg/m 3 The cost analysis was evaluated for 1 m 3 of concrete for both normal and green concrete, with the cost of construction materials taken from the Schedule of rate, Government of Tamil Nadu, Public Works Department (Government of Tamil Nadu, ). The cost analysis based on the percentage of replacement for cement and fine aggregate was performed considering 28 to 180 days compressive strength of green concrete. The cost of construction materials, such as cement, aggregates and HRWRA was considered. Since green concrete exhibited strength development as the curing increased, the compressive strength at 28 to 180 days was considered for the cost analysis. 96

2 The cost analysis was performed based on the replacement level and the compressive strength of fly ash and bottom ash in concrete. The cost analysis for fly ash and bottom ash is furnished in Table 6.1a, for 30% fly ash, 30% bottom ash and 30% fly ash with 30% bottom ash. The cost analysis of the control (normal concrete) was INR including the cost of HRWRA. The green concrete with 30% fly ash was 18% lesser than the cost of normal concrete. The cost of 30% fly ash that showed compressive strength in the range of 50 to 60 MPa was INR. The green concrete with 30% bottom ash showed 3.35% increase in the cost over normal concrete due to the higher dosage of HRWRA for the strength of 40 to 55 MPa. Similarly, the concrete with 30% fly ash and 30% bottom ash reduced 19% of the cost over normal concrete, that showed a strength in the range of 40 to 60 MPa. 97

3 Table 6.1a: Cost analysis between normal and green concrete (30 FA, 30 BA and 30FA30BA) (Binder content of 333 kg/m 3 ) Material Unit per in INR Normal concrete 30 MPa 30FA [50-60MPa] Green Concrete 30BA [40-55MPa] 30FA30BA [40-60 MPa] Cement Bag Fly ash m mm m mm m Sand m Bottom ash m water litre HRWRA litre Total cost % Savings - 18% -3.35% 19% INR- Indian Rupee, FA- Fly ash, BA- Bottom ash, HRWRA- High range water reducing admixture 98

4 Material Table 6.1b: Cost analysis between normal and green concrete (40FA, 100BA and 40FA30BA, 40FA60BA, 40FA100BA) (Binder content Unit per in INR of 333 kg/m 3 ) Green Concrete Normal concrete (40 FA) 100BA 40FA30BA 40FA60BA 40FA100BA 30 MPa [35-40MPa] [30-45MPa] [40-55MPa] [30-40MPa] [20-35MPa] Cement Bag Fly ash m mm m mm m Sand m Bottom ash m water litre HRWRA litre Total cost % Savings - 25% -7.39% 25% 9% -17% INR- Indian rupee, FA- fly ash, BA- bottom ash, HRWRA- High range water reducing admixture 99

5 The cost analysis based on the maximum percentage of replacement for cement and fine aggregate such as 40% fly ash, 100% bottom ash and the combined replacements of 40% fly ash with 30%, 60%, and 100% bottom ash was performed, considering the 28 to 180 days compressive strength and the values are furnished in Table 6.1b. The cost analysis of 40% fly ash was 1948 INR with the compressive strength at 28 to 180 days in the range of 35 to 40 MPa respectively. The concrete with 40% fly ash reduced 25% of the cost compared to normal concrete. The cost analysis of 100% bottom ash as a fine aggregate replacement was INR, with the compressive strength ranging from 30 to 45 MPa. The 100% bottom ash concrete showed an increase of 7.39% in the cost over normal concrete due to the higher dosage of HRWRA (5.59 kg/m 3 ). On the other hand, it completely eliminated the use of natural river sand in construction, that is of great importance in this study. For the green concrete containing 40% fly ash with 30% bottom ash, the cost ( INR) was 25% lesser than that of normal concrete. The green concrete with 40% fly ash and 30% bottom ash for cement and fine aggregate replacement, showed a compressive strength in the range of 40 to 55 MPa from 28 to 180 days respectively. Similarly, for 40% fly ash with 60% bottom ash, the cost was 2361 INR, that was 9% lesser than that of normal concrete, with the compressive strength in the range of 30 to 40 MPa. For the concrete containing 40% fly ash and 100% bottom ash, the cost analysis resulted in 17% increase than normal concrete, with the strength of 20 to 35 MPa. The high cost over that of the normal concrete was due to the higher dosage of HRWRA of 7.99 kg/m 3. The cost analysis for the green concrete with the binder content of 333 kg/m 3 clearly revealed, that fly ash and bottom ash can be used as cost effective construction materials as cement and fine aggregate replacements respectively, that can be designed for 25 to 55 MPa. The high cost involved for 100% bottom ash was due to its water absorption property in the concrete that increased the dosage of HRWRA, but it eliminated the use of natural river sand in construction. 100

6 6.4 COST ANALYSIS OF GREEN CONCRETE WITH FLY ASH, BOTTOM ASH AND FLY ASH AGGREGATE WITH THE BINDER CONTENT OF 389 kg/m 3 The cost analysis of the green concrete involving fly ash aggregate, includes the cost of calcium hydroxide, cement, fly ash and electric power consumed by the pelletizer for manufacturing fly ash pellets. The cost involved for the manufacturing of 100 kg of fly ash pellets was 50 INR. The cost analysis of green concrete with 30% fly ash, 30% bottom ash and 20% fly ash aggregate resulted in INR, that was 14% lesser than that of the normal concrete with INR as given in the Table 6.2. The green concrete with 30% fly ash, 30% bottom ash and 20% fly ash aggregate that attained a compressive strength of 45 to 50 MPa (28 to 180 days) reduced 14% of the cost involved in the construction. Table 6.2: Cost analysis of the green concrete with fly ash, bottom ash and fly ash aggregate (Binder content of 389 kg/m 3 ) Material Unit per in INR Normal Concrete Eco-friendly Green Concrete 30FA30BA20FAA [45-50 MPa] Cement Bag Fly ash m mm m mm m FAA 12 mm kg FAA 20 mm kg Sand m Bottom ash m Water litre HRWRA litre Total cost % Savings - 14% INR- Indian Rupee, FA- fly ash, BA- bottom ash, FAA- fly ash aggregate, HRWRA- High range water reducing admixture 101

7 The cost analysis of green concrete, clearly showed that fly ash, bottom ash and fly ash aggregate enhanced the engineering, environmental and cost effectiveness in construction, without compromising the strength and durability of the structure. This practice of construction with the replacements of cement with fly ash, fine aggregate with bottom ash and coarse aggregate with fly ash aggregate respectively, serves to be cost effective and eco-friendly green concrete. By considering the indirect beneficial effect of Green House Gas emission from the cement industry, reducing the usage of natural river sand, reduction in quarrying of natural rocks, and saving the natural land for the disposal of fly ash and bottom ash, this experimental study will be the foundation for future research. The use of fly ash, bottom ash and fly ash aggregate in construction promotes the concept of green technology in construction, that will lead sustainable development for the future generation. 6.5 SUMMARY OF THE COST ANALYSIS The cost analysis of the green concrete with the replacements of cement with fly ash and fine aggregate with bottom ash in Phase I; fly ash for cement, bottom ash for fine aggregate and fly ash aggregate for coarse aggregate replacements in Phase II is summarised below; The green concrete in Phase I with the binder content of 333 kg/m 3 reduced up to 25% of the cost over that of normal concrete, where as in Phase II with the binder content of 389 kg/m 3 it reduced to 14%. The green concrete with fly ash, bottom ash and fly ash aggregate with the incorporation of HRWRA, and by increasing the curing period, can be designed as a cost effective and eco-friendly one without compromising the strength and durability of the normal concrete. 102