Учебное пособие 2210

model, the geometric, material properties and load condition of components were inputted using the algorithm described in Fig. 2. Due to the complexity of the suspen dome structure, results for a three dimensional FEM analysis are considered to be more comprehensive and reliable than results of empirical formula.

Start

Create a model

Inputting material constants

Structural discretization

Inputting boundary conditions

Solution of simultaneous equations

Computation and graphic display

End

Fig. 2. Flowchart for the analysis

Comparison of Structural Types

The material type proposed by the author is compared with the prototype-Beijing Olympic suspen dome by (Zhang et al, 2007) in terms of internal forces, displacement and frequency.

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Static analysis

Due to the symmetrical nature of the dome structure, nodes and elements can be represented by one typical node or element. Fig 3 illustrates the nodes and elements of the dome, Fig 4 illustrates the nodal displacement for the nodes as stated in fig 3 for the suspen dome. The nodal displacement of the CFRP tensegrity are much lower than the steel tensegrity system which implies that the CFRP tensegric system of the suspen dome is more effective than the steel tensegric results obtained by (Zhang et al, 2007), it can be observed that the outer position of the nodes had smaller nodal displacement, the farther the nodes are away from the mid rib, the larger is the displacement.

Fig. 3. Numbering of nodes

Fig. 4. Comparison of nodal displacement

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Fig. 5. Comparison of Internal force of radical members

Fig 5 illustrates the internal forces in the radical members for the two dome structures which are similar; it implies that CFRP tensegric system has little effect on the internal forces generated in the radical members. In addition, it was observed that the internal force was at its largest at the outermost ring and lowest at the centre.

Furthermore, Table 4 illustrates the result obtained from the computation and comparison of the interior force in the loop truss. It was observed that there was a slight decrease in CFRP cables comparedtosteel cables by (Zhang et al, 2007) which shows thereductionof interior forces.

.

Modal analysis

The natural frequencies for the first mode carried out through modal analyses are shown in Table 5. The frequency of the structure predicts the ability of the structure to avoid collapses caused by earthquake and wind storm.

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From table 5 it can be observed that the frequency of CFRP tensegrity system is much lower than that of steel with a percentage difference of 23.8% which presents a better resistance capacity.

Conclusion

In this study, a finite element model of Beijing gymnasium suspen dome was established. Analyses were carried out to investigate the behavior of carbon fibre reinforced polymer (CFRP) cable as a constitute material. From the comparison, the following conclusions are drawn:

1)The application of CFRP by the authors is practical based on the satisfactory results obtained from the numerical analysis.

2)The concept for the application of CFRP cable is to strengthen the dome; this was proven with CFRP cables having lower nodal displacement than that of steel cables which implies that CFRP has more stiffness capability.

3)The frequency result proves that CFRP tensegrity system would successfully overcome fatigue and other harmful effect of forced vibration such as earthquake and wind storms over steel cables.

Thus, the application of CFRP cables demonstrates an outstanding performance and the results show an efficient design.

References

1.ANSYS Inc., ANSYS, (2008), Release 10.0 Documentation for Ansys, USA.

2.Behnam S., Ali D., Howlyar E., Babak P., Investigation into the behavior of suspen-dome comparison with single-layer dome, World Academy of Science, engineering and technology, 2012, vol. 6.

3.Feng Fu. Structural behavior and design methods of tensegrity domes, Journal of Constructional Steel Research, 2005, pp. 23––25.

4.Ge Jiaqi, Zhang Guojun, Wang Shu. The overall stability analysis of the suspend-dome structure system of the badminton gymnasium for 2008 Olympic Games[J]. Journal of Building Structures, 2007, no. 28 (6), pp. 22–– 30, 44 (in Chinese).

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5.Ge Jiaqi, Wang Shu, Liang Haitong. Design and research of the large-span steel structure of the badminton gymnasium for 2008 Olympic Games[J]. Journal of Building Structures, 2007, no. 28 (6), pp. 10––21, 51 (in Chinese).

6.Jiamin Guo, Shilin Dong, Xingfei Yuan. Research on static property of suspen dome structure under heap load,Advanced steel construction, 2012, vol. 8, no. 2, pp. 137––152.

7.Kitipornchai S., Kang W. J., Lam. H., Albermani, F. Factors affecting the design and construction of Lamella suspen dome system. Journal of construction steel research, 2005, vol. 61, pp. 764––785.

8.Liu Xuechun. Innovation of New-type Large-span Prestressing suspend-dome Structure System and Application of Project for Beijing Olympic Games[D]. Beijing: The College of Architecture and Civil Engineering of Beijing University of Technology, 2010 (in Chinese).

9.Subramanian N. Space Structures: Principles And Practice, Multi-Science Publishing Co Ltd, Brentwood, Essex, UK, 2006.

10.Wojciech G, Joanna K., Paulina O. Application of tensegrity structures in Civil Engineering. Procedia Engineering III, 2015, pp. 242––248.

11.Wenjiang K., Zhihua C., Heung-fai L. Chenian Z. Analysis and design of the general and outmost ring stiffened suspen dome structure. Engineering structures, 2003, vol 25, pp. 1685––1695.

12.Xu Xie, Xiao Zhang Li, Yonggang Shen, Static and dynamics characteristic of a long span cable-stayed bridge with CFRP cables, Materials, 2015, no. 7, pp. 4854––4877; doi:10.3390/ma7064854

13.Zhang Ailin, Liu Xuechun, Zhang Baoqin, Zhang Xiaofeng. Stability analysis of suspend-dome of badminton gymnasium for 2008 olympic games, Industrial construction, 2007, vol. 37, no. 1 (in Chinese).

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DESIGNING AND CONSTRUCTION OF ROADS,SUBWAYS,

AIRFIELDS,BRIDGES AND TRANSPORT TUNNELS

UDC625

Dr. Shashi Kant Sharma1, Aniruddha D. Chopadekar2,Samarth Y. Bhatia3

IMPROVEMENT IN PAVEMENT QUALITY CONCRETE BY USING POZZOLONIC MATERIALS WITH POLYPROPYLENE FIBER

Himachal Pradesh

India, NIT Hamirpur, Hamirpur, tel.: +91 8894484088, e-mail : shashi.pec@gmail.com 1Assistant professor, Department of Civil Engineering

2Student of M. Tech Civil engineering, Department of Civil Engineering 3Student of M. Tech Civil engineering, Department of Civil Engineering

Statement of the problem. Pozzolans like Fly ash and silica fume are extensively used in concrete to replace cement without affecting its strength. Micro fibers helps in controlling the cracking caused due to shrinkage of concrete, which is essential parameter to be studied in regards with pavement quality concrete (PQC).

Results. Thus the present study aims at determining combined effect of polypropylene fibers with pozzolonic materials on PQC. Fly ash, Silica fume and Polypropylene fibers in different proportion were used. The specimens were tested for compressive & flexural strength after 7, 28, 60 and 90 days. Also shrinkage test was performed after 28 days.

Conclusions. The results showed that, polypropylene fiber works well with pozzolonic materials. It was found that shrinkage reduced upto 0.6 % fiber volume with a total of 35% pozzolans. The maximum 90 day compressive and flexural strength obtained were 59.45 Mpa and 9.81 Mpa respectively and minimum 28 day shrinkage strain value of 339 was observed. Thus, combination helped in increasing the strength parameter while reducing shrinkage.

Keywords: Pozzolans, Fly ash, Silica fume, Pavement quality concrete, Polypropylene fiber.

Introduction

Pavement is a layered structure which supports the wheel loads and transfers the load stresses through a wider area on the soil sub grade beneath. The surface of the roadway should be stable and non-yielding to allow the heavy wheel loads of road traffic to move with least possible rolling resistance. Rigid pavement structure is widely used nowadays because of its dura-

© Dr. Shashi Kant Sharma, Aniruddha D. Chopadekar,Samarth Y. Bhatia, 2017

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bility and high flexural strength. A cement concrete pavement slab of specified strength characteristics are laid with or without steel reinforcement at the joints. Generally, the material used for the construction of rigid pavements is high quality plain cement concrete meant for the pavement generally called ‘Pavement Quality Concrete (PQC)’. PQC is firstly designed for the flexural and later for compressive strength. Maintaining the quality of the concrete is one of the primary objectives of ‘Pavement Quality Control program’. The tensile stresses are developed in the rigid slab due to the heavy wheel load movement. Pozzolonic materials can be used in construction of rigid pavements. Fly ash and Silica fume are the most common pozzolans used in construction. Fly ash is the waste product produced in the thermal power plants while generating the electricity using coal. The presence of fly ash in concrete makes it more flexible and the pavement constructed by using it possess higher flexural strength, there by this pavement can be classified as a semi-rigid pavement. According to the literature available on utilization of fly ash in the construction of rigid pavement, good quality fly ash can be used to replace cement by 10 to 30 percent. In this study, cement is replaced with fly ash by 10, 20 and 30 percent by weight of cement. The use of fly ash in pavement construction saves the resources which helps in achieving economy in pavement construction without compromising quality and also gives a way for disposal of fly ash.

Silica fume is used in high strength and high performance concrete. It is found to be very useful material in the concrete construction. It is very fine and highly reactive industrial byproduct obtained during the production of metallic silicon or ferrosilicon alloys. Silica fume can be obtained by the process of reduction of high purity quartz with coal in an electric arc furnace. It is composed of submicron particles of silicon dioxides. The first utilization of silica fume in concrete was reported in 1952 by a Norwegian researcher. Effect of silica fume as a cementitious material on compressive strength and workability has been studied in various studies that silica fumes increases the compressive strength while decreasing the workability. The primary role of fiber in a cementitious composite is to control cracks, increase the tensile strength and to improve deformation characteristics of the composite. There are various types of fibers available in the market like steel fiber, polypropylene fiber, carbon fiber, glass fiber etc. Steel fiber and Polypropylene (PP) fibers are most widely used in concrete mix. In this study, PP fibers were used; it has been used in cement concrete since 1960s. PP fibers are thermoplastic polymers which can be produced from the waste plastics by their recycling. PP fibers are added to concrete as secondary reinforcement to control shrinkage. It mitigates plastic and early drying shrinkage by increasing the tensile strength of concrete and bridging the

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forming cracks. The effect of PP fibers on the properties of harden concrete varies depending on the type, length and volume fraction of PP fiber. In this study PP fiber of length 6.00 mm and aspect ratio of 90 was used.

The most crucial problem associated with concrete pavements is that of cracking. Once these cracks are produced, they act as conduits for ingress of gases and water. This type of degradation of concrete results in reduction of strength and service life of pavement. The development of cracks severely affects durability property of pavements. One of the major causes of pavements cracking is plastic and drying shrinkage. Thus to check the durability performance of pavement, shrinkage test is performed in the present study.

The effect of PP fiber and Pozzolans individually with PQC has been researched upon to a large extent by many researchers previously. However the combined effect of PP fibers and pozzolans has not been studied much. Thus the purpose of this research is to study how PP fibers and pozzolans behave together to affect strength parameters and shrinkage.

Material used

The materials used in this study include cementitious material (Cement, Fly ash and Silica fume), Aggregate, PP fiber and water. To maintain the qualities of study, materials selected were tested according to the quality parameters given in the respective IS codes.

Cemetitious materials act as a binder in concrete matrix. Cement, Fly ash and Silica fume were used in this study. Pozzolona Portland Cement of 43 Grade (PPC 43), fineness 2 %, Specific Gravity 3.10, Standard Consistency 35 %, IST and FST 45 and 190 minutes respectively were used. The fly ash used in this study was brought from “Ropar Thermal Power Plant, Punjab, India”, having a specific gravity, maximum dry density and optimum moisture content of 1.784, 12.65 KN/cu.m and 26 % respectively. These properties of fly ash were evaluated by referring to IS 3812-2:2003. Silica fume of specific gravity 2.2 gm/cc was used. The PP fiber used was procured from industrial area Ludhiana, Punjab. Properties of PP fiber as specified by supplier are; Length, Aspect ratio, specific gravity, modulus of elasticity and melting point are 6mm, 90, 0.91, 3500 to 3900 N/Sq.mm and 250 0C respectively. The crushed aggregate of size 10 to 20 mm and fine aggregates of zone II of size range between 4.75 mm to 0.075 mm were taken, conforming to IS 383:1970. Locally available potable water of suitable pH range, fulfilling the requirement of IS 456:2000 was used for preparing cement concrete mix.

Mix proportion and Mix design

In this study project, ten mixtures were prepared for studying the behavior of concrete with pozzolans and PP fiber. The replacement level of fly ash with cement is 10, 20 and 30 percent and fraction of polypropylene fiber is 0.20, 0.40 and 0.60 percent of volume of specimen. A

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constant amount of silica fume i.e. 5 percent was added into all mixture excluding the control mixture. Table 1 show the mixture proportion used in this study. A concrete of M40 grade (control mix) was designed according to the guidelines given in the IRC: 44 (1976). The mix was designed in such a way that focus is given on achieving design flexural strength of 4.5 Mpa rather than compressive strength. Initial water-binder ratio of 0.43 was selected for control mix. The water-binder ratio varied according to the mix proportion selected. The specimens were cast and tested after 7, 28, 60 and 90 days of curing for Compression strength as well as flexural strength. Shrinkage strain test specimens were tested after 28 days of curing.

Experimental

Test on material used

To maintain the quality of concrete mix it is required to perform quality checking tests on the material. The quality of cement is checked as per the tests given in the IS 1489: 1991. The effect of replacing the cement by fly ash and silica fume on the properties of cement were tested in this study. For this Standard consistency test and Setting time test was performed for various mixes as given above. Similarly, the quality of Fly ash and Silica fume were checked according to the quality standards given in IS 3812 (2): 2003 and IS 15388: 2003 respectively.

SF: Silica Fume, FA: Fine Aggregate, CA: Coarse Aggregate.

Test on fresh concrete

To evaluate the workability of concrete mix, Slump cone test was performed on the fresh mix according to the guidelines and procedure given in IS 1199: 1959.

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Compressive strength test and Flexural strength test

Compressive strength test was performed on the concrete specimen. For this, the specimens of size 100×100×100 mm were cast and tested after 7, 28, 60 and 90days of curing under the standard laboratory conditions and according to the guidelines given in IS 516:1959. Similarly, the specimens of size 100×100×500 mm were cast and tested after same duration. The average of three specimens was taken as the compressive strength and flexural strength result; total 120 specimens of standard size for each test were cast and tested.

Shrinkage test

In this study drying shrinkage strain have been determined after 28 days of curing of cement composites. The drying shrinkage test was performed as per guidelines given in IS 4031 (Part 1): 1996. The specimens of size 285×75×75 mm were cast. The specimen was measured for first length reading and then the specimen were stored in lime saturated water or in a moisture room with temperature maintained at 23±2ºC. This first length reading is for information only, not to be use in drying shrinkage calculations. After 7 days of curing, specimen shall be removed and initial length reading shall be taken. This reading shall be used as the initial reading for calculation of linear dry shrinkage. After the initial reading, specimens were placed in a drying room until the age of 35 day i.e. 28 days more after initial reading. The humidity of drying room shall be monitored with the beaker method according to ASTM C 157/C157 M-04. Final reading is taken after 35 days. Then the shrinkage strain is calculated according to equation (a).

Linear Shrinkage Strain = [(L-l))/L] × 100,

Where, L = Original length of specimen; l = Length of specimen after 28 days.

The average of three specimens is taken as the Shrinkage strain; total 30 specimens of standard size as mentioned above were cast and tested.

Results and discussion

As per IRC58: 2011, concrete design is based on 28 day strength. But in case of concrete pavement, 90 days strength can be permitted in view of the fact that during initial period of 90 days, the number of repetitions of load is very small and has negligible effect on cumulative fatigue damage of concrete. Hence in this study a comparison is made between the strength parameter at 90 days. The test results are given in Table 2.

Standard Consistency and Setting time of cement paste

The effect of replacement of cement by fly ash and silica fume on consistency of cement paste is represented in table 2. It can be observed from the results that normal consistency of control

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