METHOD OF PRESTRESSING CONCRETE WITH BAMBOO

Technical Fields

Construction Engineering

Argiculture (Bamboo)

Background Art

Concrete is a hard but brittle material, it can withstand high compressive force but can resist only very low tensile force. Therefore it will normally not be designed to withstand any tensile force. Reinforcing steel is used in the steel reinforced concrete to withstand the tensile force. However concrete must be pulled to stretch out be so that the tensile force can be transfered to the reinforcing steel. This causes cracks concrete and lets waits leak into concrete mass, which shortens life of reinforcing steel in concrete. That? are generally 2 types of Prestressed Concrete with steel wire.

1 , Pretcnsioning Ptestressed Concrete. First, steel wires are {railed in a formwork.

Then concrete is casted over. When the concrete is hard, steel wires are Cut at their both ends. After cutting of steel wires, they will shrink back causing the concrete to be compressed.

2. Postenshming Prestressed Concrete. First, pipes ate place in a formwork. Then concrete is cast over. Steel wires are insert through installed pipes. When concrete is hard, steel wires are pulled. Afterwards, pulled Steel wires are cut and wedgged at thiis both ends. The both end anchorages of steel wires will compress comcrete mass. Prestressing or compressing of concrete results in reduction of concrete cracks. Prestressing concrete with steel wire works well. However using bamboo instead of steel is more environmental friendly. Unlike iron ore, bamboo is a natural material that will never be depleted.

The use of bamboo to reinforce concrete has been Thai wisdom. However reinforcing concrete with bamboo with conventional methods has some problems such as:

1. Natural concrete has many pores, which allows water leaking into concrete mass. As a result, reinforced bamboo decays and is not tong lasting. From the research of Chatsirikul (1980), lie concluded that moisture transfer between bamboo and concrete is a major cause of deterioration of the bond between bamboo and concrete. This is a problem in bamboo reinforced concrete structural or non-struclural member.

2. Pores of concrete and cracks of concrete from elongation, that bamboo can be activated to withstand tensile forces, allow tiny insects entering into concrete mass. They eat and destroy reinforced bamboo.

3. Pores of concrete and cracks of concrete from elongation, that bamboo can be activated to withstand tensile forces, make Bamboo Reinforced Concrete be susceptible to fire.

4, Pores of concrete allow water in reinforced bamboo evaporating through Continuous pores. This causes shrinkage of bamboo and loss of interconnection between bamboo's and concrete's surfaces. Eventually, tensile forces can not be transferred to reinforced bamboo.

The mentioned problems can be solved by prestressing concrete with bamboo. Ibis solves the problem of continuous porosity in concrete.

The process of prestress ing concrete with bamboo from tins patent can solve the mentioned problems of Bamboo Reinforced Concrete. Additionally, this process has never been invented by other inventors and has never been disclosed before. Description and Purpose ofthe Invention

Tite purpose of this in vention is to produce products made from the process of prestressing concrete with bamboo, as described in this patent. ^' Ibis process makes Bamboo Reinforced Concrete more durable and has a longer service life. Additionally, it solve the problems of Bamboo Reinforced Concrete, such as separation of bamboo from concrete.

This invention is about methods to prestress concrete by using bamboo to solve the problem Of Bamboo Reinforced Concrete, which is not durable.

There are generally 2 methods of prestressing concrete with bamboo. The first method is “Pretension", which bamboo is pulled before casting of concrete. The second method is “Posttension”, which bamboo is pulled after casting of concrete. After the process of prestressing, concrete and bamboo will work together as a composite material. Prestressing forces from bamboo compress concrete mass, resulting in compression in concrete body. Thus, this reducs cracks and pores in concrete.

This patent

1. identifies the most suitable native bamboo species in Thailand for using in the process of prcsfressing concrete.

2. discloses methods prestressing concrete by using bamboo in order to solve the existing problems of Bamboo Reinforced Concrete. There are 2 methods of prestressing concrete with bamboo. The first one is“Pretension", which bamboo is pulled before easting of concrete. The seeone is“Posttension’’, which bamboo is pulled after casting of concrete.

Reference

Chatsirikul, U. 1980. Behavior of a concrete floor-joist system reinforced with flint coated bamboo. Master Thesis, Faculty of Engineering, Chulalongkom University, Bangkok. Disclosure of Invention

1, The most suitable native bamboo species in Thailand for prestressing of concrete are Thyrmsiachys siamemis Gamble and Thyrsostaehys oliveti Gamble,

2. Two methods to produce products or structural members dr non-structural members from Bamboo Prestressed Concrete or Bamboo-rei nforced Presiresscd Concrete are described as followed:

2.1. first method “Pretension” or “Bamboo-reinforced pre-tensioned Concrete ¹ ' is described as followed:

2.1.1. Prepare dead weights, listening devices and fasterrer/wedge/holder for bamboo ends (1 ). Additionally, weight platforms (3 ), hydraulic jacks (5) or bamboo end pullers (5) or or bamboo fiber pullers (5) and hollow pipes (2) are prepared on the floor or concrete formwork

(6).

2.1.2. Prepare bamboo by longitudinal splitting bamboo. Longitudinal splitted bamboo needs not be trimmed around joints of bamboo. This step can also prepare bamboo into fibre. Put bamboo/bamboo fibre into concrete formwork. At one end, there is bamboo/bamboo fibre end holders or wedges (4). At another one, there is bamboo/bamboo fibre puller (5) or hydraulic jacks (5).

2.1.3. Fill all bamboo ends (1) to disallow water and air into the bamboo trunks/culms/fibrre with waterproof materials.

2.1.4. Ml bamboo/bamboo fibre by bamboo end pullers or hydraulic jacks (5). By increasing the pulling force until it readies the specified tension. This specified tension force is held (by bamboo end wedges) at one of the values in the range of 10 - 99% of the maximum tensile strength of bamboo/bamboo fibre. Naturally, pulling of bamboo can be undertaken at only one end or it can be done on both bamboo/fibre ends as shown in Figure 1.

2.1.5. Cast concrete (7) over positioned bamboo, which will later work to withstand forces in concrete as a composite material, as shown in Figure 2. 2.1.6. Leave concrete to solidify and to have good bonding between concrete and bamboo/bamboo fibre. Concrete (8) has to strong enough not to be damaged from the process in step 2.1.7. The period of time for concrete to fully harden ranges 3 - 28 days depending on concrete mixtures.

2.1.7. Release pulling forces from bamboo/bamboo fibre. Cut the bamboo ends (I 4) to equal length of concrete as shown in Figure 3 . The bamboo can be cut to be shorter than concrete in the ease of a hole for bamboo/bamboo fibre are prepared in concrete ends. The bamboo can be cut to be longer than concrete, if wanted. At this step, the cut bamboo shrink itself because it was pulled and elongated (pre-tensioned). This contraction is also cause the concrete to shrink because bambpo/bamboo fibre transfer compressive forces into the concrete mass. Tilts causes compressive fiances in concrete

(10).

2.1.8. Plug or seal all bamboo ends (1) and/or coat protruding bamboo surfaces to disallow water or air entering or leaving bamboo. Another purpose is to protect bamboo from insect, as shown in Figure 4. The product is a structural or nonstructural member from Bamboo-reinforced Prestressed Concrete (9).

2.2, The second method“Posttension” or“Bamboo-reinforced post-tensioned Concrete” is described as followed:

2.2.1. Prepare hollow metal pipes (2) with their holes larger than spiitted/imsplited bamboo culms or bamboo fibre, which will be used as concrete reinforcement. These pipes must have good adhesion or bonding with concrete. Put pipes in particular positions that concrete needs bamboo reinforcement as shown in Figure 5.

2.2.2. Prepare bamboo by longitudinal splitting bamboo. Longitudinal sp lifted bamboo needs not be trimmed around joints of bamboo, This step cam also prepare bamboo into fibre. Put bamboo/bamboo fibre into concrete formwork. At one end, there is bamboo/bamboo fibre end holders or wedges (4), At another one, then? Is bamboo/bamboo fibre puller (5) or hydraulic jacks (5),

2.2.3. Put bamboo/bamboo fibre (1 ) through the prepared metal pipes (2) before easting of concrete as shown in Figure 6 . Alternatively, bamboo/bamboo fibre can be put through the pipe after hardening of casted concrete. If bamboo is not long enough, 2 bamboo can be wrenchingty tied together at their ends with bamboo strip. Any connection need at lease 2 wrenghing points.

2.2.4. Casting concrete (7) over pipes for bamboo (except pipe ends protruding from concrete) as shown in Figure 7.

2.2.5. Leave concrete to solidify mid to have good bonding between concrete and bamboo/bamboo fibre. Concrete (8) has to strong enough not to be damaged from the process in step 2,2.6. The period of time for concrete to fully harden ranges 3 - 28 days depending on concrete mixtures.

2.2.6. Pull the bamboo in the pipe embedded in the concrete with bamboo end pullers (5) or hydraulic jacks (5) as shown in Figure 8. Hold the pull force at a certain value in the range of 30 - 99% of the maximum tensile strength of bamboo/bamboo fiber. Naturally, bamboo end pulling can also be done at both ends of bambooAmmboo fibre

2.2.7. Increase the pulling force to the specified tensile strength of bamboo/bamboo fibre, This value ranges from 10-99% of the maximum tensile stress of bamboo/bambop fibre. Hold the pulling force at this value.

2.2.8. Cut the bamboo «ids (14) and insert the wedge at the ends (4). At this step, the cut bamboo shrink itself because it was pulled and elongated (post-tensioned). This contraction is also cause the concrete to shrink because bamboo/bambOo fibre transfer compressive forces into the concrete mass. This causes compressive forces in concrete (10). 2.2.9. Plug or Seal all bamboo ends (1) and/or coat protruding bamboo Surfaces to disallow water or air entering or leaving bamboo. Another purpose is to protect bamboo from insect, as shown m Figure 9. The product is a structural or nonstnictural member front Bamboo-reinforced Prestressed Concrete (9).

2.2.10. Inject cement plate or other durable substances, that has good braid to both bamboo surface and metal tube surface, in to the pipes with bamboo inside, (litis step explained in 2.2.10 can be skipped. However it will increase durability of bamboo).

2.2.11. Leave until concrete plate or other substances from 2.2.10 strong enough in order Id achieve die state of composite materials between bamboo and concrete. Eventually, the product Or structural member or non-slruciura! member from Bamboo -reinforced Prestressed Concrete (9), as shown in Figure 10, can bear loads or withstand forces.

Best Mode ef Carrying oat the Invention

The same as described in the topic“Disclosure of Invention”.