GB2367586A - Construction process for low energy buildings - Google Patents

Abstract

A wall is cast between inner <B>21</B> and outer <B>17</B> polystyrene forms. The boards are supported against lateral pressure due to the liquid walling material by wire ties <B>23</B> and plate members <B>26</B>, <B>27</B>. The inner surface of the outer form <B>17</B> is treated, textured or profiled to bond to the walling material, the outer form <B>17</B> remains in place as thermal insulation for the building. The inner surface of the inner form <B>21</B> is wrapped in polythene film <B>22</B> as a release membrane, the inner form <B>21</B> is removed once the walling material has cured. The inner surfaces of the inner <B>21</B> and outer <B>17</B> polystyrene forms are moulded or cut to provide vertical rebates so as to mould monolithic piers to buttress the wall. The outer surface of the outer form <B>17</B> is textured to resemble traditional building materials. The walling material may be low density or quick setting concrete, earth with or without straw, or layered wet mixed calcium sulphate.

Description

Patent application-19 July 2001 FormPat7, with priority ofFormPat6. lwp of 23 July 2000. D. H.

Stephen Tir Gaia Solar Village, Rhayader, Mid Wales, LD6 5DY, 01597 810929 Construction process for low energy buildings.

This invention relates to the technical field of building construction, and particularly to the use of expanded polystyrene (EPS) as formwork for in-situ concrete to provide well insulated housing appropriate for the future in requiring little fuel input for space heating in winter.

Domestic fuel prices are likely to rise steeply with the UK expecting to require gas imports in about five years, and oil deposits being depleted. Traditional houses have many shortcomings which waste fuel: 'Many interconnecting passages are formed by gaps in joints, perforations in bricks and block, wall cavities and timber joist floors that allow external air to percolate through a house. This makes it impossible to control loss of warm air.

'Air infiltration through and around cavity insulation impairs its insulation value.

'The thickness of thermal insulation that can be accommodated in a wall cavity is insufficient for future needs. A wider cavity would further impair the already inadequate structural stability of brick and block cavity walls, which do not meet modem structural performance requirements.

'brickwork is cooled by the evaporation of absorbed rain, giving the effect on heat loss of a climate several degrees colder.

Cavity insulation results in the external brickwork being colder.

Cavity insulation restricts air circulation and drying, and results in brickwork being wetter, colder and more vulnerable to frost damage.

Driving rain, which is likely to be more extensive with climate change, may saturate the external leaf, wet the cavity insulation and bridge the cavity to wet the inner leaf.

"Cold bridges"at lintels, etc. inherent in the construction method short circuit cavity insulation in many places.

The construction and ventilation requirements of traditional pitched roofs make air sealing of the living space difficult.

- Timber moves with changes in humidity such that gaps are likely to open in timber floors, roofs, and frames.

The small thermal storage capacity of lightweight concrete block walls, timber floors and frames restricts utilisation of solar heat gain.

In-situ concrete has fundamental advantages for low-energy buildings : Effectively jointless construction without cavities or perforations achieves good air sealing to minimise heat loss from adventitious exfiltration of warm air and allow controlled ventilation with heat recovery.

100% effective thermal insulation can be provided by casting concrete against EPS, to which it bonds as it sets, and which is impermeable to air, preventing air blowing through or around the insulation.

The high thermal capacity of concrete can absorb and store solar gains, to obtain maximum contribution to heating from solar gains in winter and to stay cool in summer without air conditioning.

Concrete construction usually requires the fabrication of a container into which newly mixed concrete is placed. It then sets by hydration of the cement, acquiring permanently the shape of the container. Such containers are known as moulds, shutters or generically, forms or formwork, and are structurally supported by falsework This invention relates mainly to in-situ concrete construction where formwork is assembled successively at the required positions of the building elements, and the concrete is cast and hardens in place to construct the building.

Formwork must be strong and rigid to resist displacement during placing and compaction by the hydrostatic pressure of the semi-liquid concrete. The form face which provides immediate support for the lateral pressure of the concrete is usually plywood, but this deteriorates rapidly in contact with the abrasive alkaline concrete, such that it may be used only a few times. For greater durability steel may be used, but is more expensive and heavier.

The costs of making or hiring, erecting and dismantling such formwork for in-situ concrete construction is about half the total cost, which may negate potential savings over labour-intensive brickwork.

Proprietary systems of EPS wall formwork are available, which are left in place to form the thermal insulation to the wall and reduce the labour costs. These consist of relatively small mouldings similar to EPS packaging, which are erected to create a cavity to receive the concrete to form the wall. Such systems have extended the potential of concrete construction, but several problems remain: 'The mouldings and accessories are relatively expensive which may make construction more expensive than traditional.

'The ties between opposing sides required to resist the lateral pressure of the concrete are usually attached in such a way as to depend on the shear or tensile strength of the relatively weak EPS. Even high density EPS formwork may burst if the pressure developed is too high.

* Concrete can be placed only in small increments of height and must be allowed to set before the next lift to avoid developing insupportable pressure. This may preclude the use of ready mixed concrete, which is typically delivered in truckloads of six cubic metres, and is usually preferred to site mixing.

* The EPS bridges in some systems and many ties obstruct placing of the concrete.

'A layer of EPS remains attached to the inner face of the wall, which nullifies the thermal admissivity required for a passive solar heated building.

* For adequate fire resistance in the finished building especially where the concrete is bridged by EPS, an internal lining of plasterboard may be required to be mechanically fixed through the EPS layer to the concrete.

The present invention has the following advantages : Large thick sheets of EPS can be used as permanent formwork to provide 100% effective super insulation in the optimum external location. Thermal bridging is virtually eliminated.

The EPS sheets used to form the inner faces of external walls would usually be treated to release from the concrete, which would be finished with plaster to leave a high thermal admissivity surface, to absorb and conserve heat gains from the Sun, equipment and people, as required for passive solar buildings. Good external insulation plus the high thermal capacity of the structural wall averages out extreme day and night temperatures. Little heat input will be needed to maintain comfort.

The relatively thick EPS sheets are sufficiently stiff to support the hydrostatic pressure of the concrete with reasonable spacing of ties.

* The lateral pressure of the concrete can be reduced by reducing the density of the wet mix, by replacing sand, gravel or crushed rock, with a lightweight structural aggregate such as sintered pulverised fuel ash and mixing a non-structural material such as expanded polystyrene beads, alginate jelly balls, or air with air entraining or foaming agents to form cavities in the hardened concrete.

* Ties can be provided inexpensively by piercing the relatively soft EPS form faces with wire or plastic attached to plates which spread the tension of the ties, enabling the EPS to support it in compression.

'The thin ties offer little obstruction to placing the concrete.

* On external faces, the ties may have a further use of fixing vertical framing or battens to

support a weatherproof cladding, as of hanging tiles, timber shiplap, or render.

Sprinkling water absorbent particles such as dry lightweight aggregate into the form to absorb water and stiffen the concrete while it is being placed allows the whole height of the wall to be placed in a short time and thus enables full truck loads of ready mixed concrete to be used.

* Where the floor above is to be concrete, the falsework supporting the floor also supports the wall forms, avoiding the need of separate bracing and providing a safe working platform while placing the wall concrete.

Fixing of insulation and air tightness is achieved during construction without need of vapour barriers, breather membranes, mechanical fixings, adhesives, sealants, injection or spray equipment, etc.

'Consumption of timber, much of it tropical hardwood, used as formwork in concrete construction throughout the world and burnt after a few uses can be greatly reduced. The EPS forms replace plywood and timber forms. The EPS is eventually used as permanent insulation for the roof or elsewhere. EPS can suffer much physical damage and soiling without significantly impairing its insulation value. Vertical framing members are reused as studding for plasterboard internal walls.

* Labour costs of erecting and striking formwork are greatly reduced. The technique largely avoids heavy manual work, can use relatively unskilled labour and is suitable for self builders.

* EPS thermally insulates the concrete while it is setting and hardening, protecting it from frost damage, and conserving the heat of hydration of the cement, accelerating the hardening, and allowing more pulverised fuel ash to be added, which reacts relatively slowly.

Better structural stability than a cavity wall is obtained with a solid wall even with low strength materials. Buttresses can be formed in the wall.

The technique can utilise several waste materials. Pulverised fuel ash from coal burning power stations is sintered into a lightweight aggregate which can replace sand gravel or crushed rock, reducing quarrying. The lighter weight reduces pressure on the form faces, facilitating this construction process.

The technique can save resources by utilising lower strength materials which are adequate for structural load bearing walls. Concrete can be foamed, or incorporate expanded polystyrene beads. Crushed brick or glass, and whole bottles, empty or filled with water to increase thermal capacity, can be entombed in a wall, but compatibility needs to be confirmed.

Sulphate resisting cement may need to be used with crushed brick.

* A concrete wall kept dry and warm behind a renewable cladding and insulation, is almost indefinitely durable and invulnerable to wood boring insects, rot, fire, hurricanes and floods.

* Traditional materials such as cob or rammed earth, with or without the addition of a binder such as Portland cement can be used as the walling material. Such materials may be too water sensitive for conventional walling, being eroded by rain, but can be utilised for structural walls kept dry by the cladding and EPS.

'Calcium sulphate, which may be too water soluble for frequently wetted walls, produced as a waste product of flue gas desulphurisation, can also be used as a fast-setting structural walling in place of Portland cement concrete.

A continuous structure, reinforced with metal, bamboo, straw, etc and kept dry should be more structurally stable and resilient than brick and blockwork, perhaps providing affordable earthquake resistant housing.

According to the present invention, there is provided a construction process including some or all of the following: Where the floor or roof above is to be of in-situ reinforced concrete or other structure requiring temporary support, conventional floor falsework is first fixed in position, and also used to support and align the wall formwork and provide a working platform to facilitate placing the walling material in it.

The form faces supporting the walling material during placing are composed of a cellular plastic material of sufficient mechanical strength and thickness to resist with suitable intermittent support of the reverse side and with acceptable deflection the pressures imposed during placing of the walling material.

Where the cellular material is to remain in place to provide external insulation to the building, the form faces are textured, profiled or treated with a bonding agent, to remain attached to the hardened walling material.

The outermost face of the cellular material may be moulded in such a way as after applying a weather resistant finish it simulates timber shiplap, stone, brick or other aesthetically appealing texture.

The form faces moulding the internal surfaces of walls, are wrapped in a plastic film or treated with a suitable agent to release easily from the walling material after it has hardened.

The cellular plastic sheets may be moulded, cut or of differing thicknesses to provide vertical rebates so as to mould monolithic piers to buttress the wall, and allow the structural wall over much of its area to be thinner than otherwise required for a wall of uniform thickness and the insulation to be thicker, while minimising the overall wall thickness.

The opposing cellular form faces are tied together to resist the lateral pressure of the walling material during placing with ties attached to stiff members or plates supporting the reverse surface of the cellular form face, so distributing the reaction of the ties to support the cellular material in compression and limiting its stress concentration and deflection.

The construction process may utilise wet mixed walling material such as concrete or calcium sulphate, or materials such as rammed earth, soil cement, or dry mix concrete placed substantially dry. In each case ties are provided to limit the lateral pressure developed to what can be safely supported.

In the common case of ordinary Portland cement concrete, which sets relatively slowly, the mix may be induced to stiffen and support its own weight more quickly by distributing water absorbing particles such as dry lightweight aggregate concurrently with wet mix.

The walling material may be lightweight, as made by replacing dense sand, gravel or crushed rock with pumice, sintered pulverised fuel ash or other strong aggregate, or by introducing cavities as by air entraining or foaming agents, or expanded polystyrene beads, so also reducing the lateral pressure.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing.

Figure 1 shows a vertical cross section of wall and floor formwork at 90 degrees to the faces of the wall being constructed.

Figure 2 shows a plan of the wall formwork.

Referring to figure 1, conventional floor falsework and formwork is erected on the previously-constructed floor 1 consisting of tubular vertical stanchions or adjustable props 2 and 7 and braced with lacings 9, plus scaffold tube walings 10, at the calculated distance to correctly locate and plumb the wall 8, with supports for the floor concrete 6 of timber ledgers 3, joists 4 and plywood form face 5.

The wall formwork is then located consisting of a prefabricated framework of vertical studs 13, the inner EPS form face 21 pre-wrapped in polythene film 22 as a release membrane, inserts (not shown) to form window and door openings, wall reinforcement 16 and outer EPS form faces 17, temporarily spaced apart by battens 20 which are withdrawn as concreting proceeds.

Pairs of ties 23 are made by pushing plastic coated otherwise releasable wire from each side of the scaffold tube walings 10. Wherever the wires emerge plywood plates 26 followed by a smaller steel plate 27 each with a central hole are placed over the wires, which are tensioned and secured by spot welding to secure the formwork assembly vertically to the falsework, and resist the lateral pressure of the concrete. Further ties are inserted especially from the outer face through long strips of plywood 25 placed over joints to align the external faces of the EPS and provide more support where its thickness is reduced to form buttresses 15.

Suitable means are provided as by tensioned wires (not shown) through the concreting cavity from end to end to tightly close the vertical joints between adjacent EPS form faces, and resist the longitudinal pressure of the concrete.

The floor above may also be prepared for concreting, with reinforcing steel fixed with spacers, inserts and conduits, followed by walking boards (not shown) to allow concreting to proceed without a break from wall to floor.

The concrete mix is designed to be substantially self-compacting in the walls, but meeting the strength requirements of the suspended floor.

The quantity of lightweight aggregate or other water absorbent particles required to stiffen the concrete mix is predetermined by calculation or experiment, and appropriate quantities pre-measured and positioned around the top of the wall formwork, with a suitable funnel or other device not shown to control the flow of particles. The particles are well distributed during the placing of the walling concrete.

The first part of a delivery of ready mixed concrete may be placed directly into the form to a limited height and compacted by hand tamping. The remaining concrete may be spread to the required depth and compacted on the floor formwork, but leaving working space near the wall forms clear until last.

When the floor concrete 6 has gained adequate strength, the wire ties 10 are cut and or pulled from the concrete and the falsework and formwork 2,3, 4,5, 7,9, 10 is removed, followed by the inner polythene-wrapped EPS form face, holes, and after making good any defects, the wall is finished internally with plaster, and externally with an acrylic paint, reinforced coating or other weather resistant finish.

Claims (10)

1. Claims 1 A construction process using relatively large thick boards of cellular plastic of sufficient strength and thickness as the facing boards of wall formwork to support with acceptable deflection the pressures developed during placing of a mouldable walling material with intermittent support of the reverse sides of the cellular plastic in compression
2. 2. A construction process as in claim 1 wherein the surface of the cellular plastic form adjacent to the walling material is treated, textured or profiled to permanently bond to such wall.
3. 3. A construction process as in claim 1 wherein a surface of the cellular plastic adjacent to the walling material is prevented from bonding by lining the face with a suitable membrane or coating
4. 4. A construction process as in claims 1, 2 or 3 wherein the reverse surface of the cellular form is textured to simulate timber shiplap, stone, brickwork or other relief which after an appropriate finishing treatment presents an aesthetically acceptable appearance.
5. 5. A construction process as in claims 1,2, 3 or 4 in which the form face is cut or moulded over a proportion of its length to form piers or buttresses monolithic with the walls.
6. 6 A construction process as in claim 1,2, 3,4 or 5 in which the opposing cellular forms are tied together to resist the lateral pressure of the walling material by piercing the cellular plastic and threading through from one side a wire or string of adequate tensile strength, secured at each end to a plate or member of stiff material to resist the tension in the ties by acceptable compressive stress of the cellular plastic.
7. 7. A construction process as in claims 1,2, 3,4, 5 or 6 wherein the walling material is concrete which is reduced in density by use of a load-bearing lightweight aggregate, non-load bearing particles such as expanded polystyrene beads or air
8. 8. A construction process as in claims 1,2, 3,4, 5,6 or 7 in which concurrently with the wet mixed walling material water absorbent particles are placed in the formwork such as to cause the mix to stiffen relatively quickly, so reducing the lateral pressure.
9. 9. A construction process as in claim 1, 2,3, 4,5, or 6 in which the walling material is mixed dry and placed in the form and sprinkled during placing with sufficient water to hydrate the binder, but not enough to fluidise the mix or cause excessive lateral hydrostatic pressure 9 A construction process as in claims 1,2, 3,4, 5 or 6 in which a walling material such as a suitable earth with or without straw is placed dry or moist and coheres without addition of a binder
10. 10. A construction process as in claims 1,2, 3,4, 5 or 6 in which wet mixed calcium sulphate with or without addition of inert aggregate is used as a walling material placed in successive layers and allowed to rapidly set and gain strength before the next layer is placed 11 A construction process as in claim 1 in which one cellular plastic form remains permanently attached to the walling material as in claim 2 providing external thermal insulation to the building and the inner plastic form releases as in claim 3 and where the walling material is ordinary concrete or lightweight concrete as in claim 7 and water absorbing particles are distributed in the concrete as it is being placed as in claim 8.

    12 A construction process substantially as described herein and by reference to figures 1 and 2 of the accompanying drawings