Damage Repair of Ferrocement

Common types of damage

Ferrocement structures shall be inspected, as part of a regular maintenance programme, to detect any of the following types of damage. Appropriate repair measures shall than be taken.

Delaminations

Delaminations occur when ferrocement splits between layers in laminated constructions due to springing back or bridging of the mesh during construction. Delamination sometimes occurs at or near the neutral axis under impact or flexure when there are many voids in the interior layers. Such areas give of a hollow sound when taped with a hammer or stroked with a steel bar.

Spalls

A spall is defined as a depression resulting when a fragment is detached from a larger mass by a blow, by the action of weather, by pressure, or by expansion within the mass. Spalls shall be considered large when their size exceeds approximately 20 mm in depth or 150 mm in any dimension, and shall be repaired by replastering.

Spalls are usually caused by corrosion of steel, which causes an expansive pressure within the ferrocement. Chlorides in the concrete greatly increase the potential for corrosion of the steel. Under such conditions, continued spalling is lightly and the repair of local spalls areas may even promote the deterioration of the concrete because of the presence of dissimilar materials.

An area of steel corrosion and chloride contaminated concrete may be considerably larger than the area of spalled concrete, and the full area of contamination rather than the spall itself shall be Broken and replastered.

Fire damage
Ferrocement may be more susceptible to fire damage than conventional concrete because of thin cover.

If the fire were intense enough to release the amount of chemically bound water in the cement, destroy the bond between the cement and the aggregate, or oxidize the reinforcement, the surface would be charred and spalled so that the damage could be easily identified. Full scale removal and repair shall than be required.

Cracks and Local Fractures

Hairline cracks and crazing due to temperature changes or drying shrinkage in the cover coat do not require repair. Continuous wet curing will cause autogenous healing, and a flexible coating will conceal the crack from view. If cracks are caused by continuing overloads or are due to structural settlement and the cause cannot be removed, replacement or a structural overlay shall be required. Cracks due to occasional impact or overload may be repaired. Local fractures are cracks in which displacement of the section has occurred as a result of impact.

Evaluation of Damage

Evaluation of damage shall take into consideration its extent, cause, and likelihood of the cause still being active. The method of repair shall be dictated by the the type of damage, the availability of special equipment and repair materials, and the level of skill of the workers employed. Economic factors may influence the decision as to whether the repair shall be extensive and permanent, or limited in scope in response to an immediate problem.

Repair materials shall bond to the original structure, resist pollutions in the surrounding soil, water or air, and respond the same way to changes in temperature, moisture, and loads. Removal of deteriorated or chloride contaminated mortar trapped within the reinforcing mesh requires a large amount of hand labor, so it may be economical (and better for long term durability) to reconstruct or replace an entire area using the original structure as a form that can be left in place or removed after the overlaid structure has cured. Complete reconstruction shall be undertaken when chloride contamination, mesh corrosion, and deterioration of the mortar are extensive.

Testing for damage in ferrocement may be done by tapping with a hammer to break into any voids under the surface, or by drawing a metal bar over the surface and listening for sounds indicating voids or the presence deteriorated concrete. A high quality ferrocement should produce a bell like sound and resist moderately severe hammer blows without damage.

Surface Preparation for repair of damage

The primary adjective is to remove any deteriorated mortar or mortar contaminated with corrosive agents and to provide a surface to which the repair materials can be bonded properly. The rougher the surface, the greater the area available for bonding.

Removal of Deteriorated Concrete

As a first step in any repair or disintegrated, unsound, and contaminated mortar shall be removed. Saws and chipping hammers used for conventional concrete shall not be used for ferrocement unless large sections are to be completely removed.

Small areas shall be prepared by hand hammering just hard enough to pulverize deteriorated or cracked mortar, but not to the point of damaging the reinforcing mesh.

A pneumatic needle gun may be used for cleaning out broken ferrocement, opening out cracks and roughening the surface.

Particles of sound mortar embedded in the mesh need not be removed provided they are small enough not to interfere with the penetration of new mortar and they project from the finish surface.

Reinforcement

Any loose, scaly corrosion revealed on cleaning out the mortar shall be removed by sandblasting, water jet, air blasting, or vacuum methods.

An alternative method for removing rust is to brush naval jelly or spray dilute Phosphoric Acid over the repair area and flush thoroughly.

Where the mesh case has been displaced but is still intact, it may be pushed or jacked back in place and supported securely to withstand the pressure of applying the repair material. Where the reinforcement has been torn, the old mesh shall be laced back to close the opening.

When rods supporting the mesh is are torn they shall be spliced by a 15 diameter overlap of the partner rod or anchored by hooks.

Fire Protection Plumbing

Water required for interior fire protection

The minimum quantity of water for sprinkler and hose use within the building according to their occupancy classification shall be in accordance with table -1 indicating fire protection flow requirements or on the basis of the hydraulic design of the system.

Water source for fire protection 

Water required for interior fire protection of a building shall be supplied from one or a combination of the following sources:

Table-1 : Fire Protection Flow Requirements

Building Type	Sprinkler System (l/min)*	Standpipe and Hose system (l/min)*	Duration** (min)
Light hazard - I	1000	1000	30
Light hazard - II	1900	1900	50
Ordinary hazard - I	2650	1900	75
Ordinary hazard - II	3200	1900	75
Ordinary hazard - III	4800	1900	75
Notes: * Values will be for one riser serving floor area of 1000 m2. **These duration shall be for a building up to the height of 51 m. For greater height of 51-102 m and above 102 m, the duration will be 1.25 times and 1.5 tomes of the specified values respectively. Light hazard – I : Occupancy groups, A1, A2, A4 Light hazard – II : Occupancy groups, A3, A6, A8, B, C, D, E4, E7, F1 & F2 Ordinary hazard – I : Occupancy groups, E1, E3, E5, F3, F4, F5, F6, F7, G1 & G4 Ordinary hazard – II : Occupancy groups, G2 & H1 Ordinary hazard – III : Occupancy groups, G3 & H2 Extra hazard : Occupancy groups, j – pressure and flow requirement for this group shall be determined by Fire Department but shall not be less than required value for Ordinary hazard-III

Direct connection to water main

For continuous water supply (public water supply system or independent system only for fire protection) with sufficient quantity and pressure to feed fire fighting equipments during peak demand period, direct connection of the fire fighting system to the water main may be adopted (Fig-1).

Roof gravity tanks

For water supply system with inadequate quantity or pressure during peak demand period but with sufficient pressure to feed roof tank, a roof gravity tank shall be provided to feed fire fighting equipments(Fig-2).

Storage tank

For water supply system with inadequate pressure to feed fire fighting equipments or roof gravity tank, the building premises shall have a ground ( or under ground) tank to store water for fire fighting and one of the combination shown in Fig 3,4,5 shall be adopted.

The system only for fire fighting purpose may be designed with automatic fire pump as shown in Fig 3. The water supply system for domestic use and fire protection may be designed with roof gravity tank and manually controlled pump as shown in Fig 4. The pressure tank with automatic fire pump and the compressor may be used for supplying water to the fire fighting equipment as shown in Fig 5 and Fig 6. The location of the pressure tank shall be such that it will provide the required pressure at the highest fire fighting equipment.

The water stored in storage tank for fire fighting operation shall be used for other purposes ( see Fig-7).

The ground storage tank shall be easily accessible to fire engine of fire Department. In absence of space available for fire engine, the cover slab of ground storage tank shall be designed to withstand a vehicular load of local fire engine.

Individual Water sources

In absence of public water supply system, the building premises shall have individual water sources as specified in the post linked here. The individual water sources with adequate yield during peak demand period will serve as a fire service ground tank as shown in Fig-3, Fig-4, Fig-5. Otherwise, the water of the individual sources shall have to be stored in a tank as specified in storage tank section.

Design consideration for Standpipe and Hose System

1.The fire protection system shall be designed for their effective use either by amateur or trained fire fighting personnel or both.

2. All standpipes in standpipe system shall be sized so that they will provide a minimum flow specified in Table-1. In standpipe system with more than one standpipe, the supply piping shall be sized for the minimum flow specified in Table-1 for the first standpipe plus 1000 litre per minute for such additional standpipe. The total number of such additional standpipes shall not be more than 8. All standpipe risers shall be connected through a gate valve with a main of size equal to that of the largest riser.

3. The minimum pressure for standpipes supplying a 50 mm or larger hose shall be at least 300 Kpa. For standpipe supplying first aid hose (38 mm nominal) may have a minimum pressure of 200 Kpa.

4. The size (diameter) of stand pipes for various building height may be as shown in Table -2 or hydraulically designed to provide the required flow and pressure, stated above, at the topmost outlet.

Table-2 : Standpipe Sizes

No. of Storeys	Building Height(m)	Size of Stand pipe(mm)
Up to 5	UP to 17	75*
Up to 10	UP to 33	100
10 to 20	33 to 63	150
20to 54	63 to 65	200

*These pipe may be used only for occupancy groups A1, A2 and A4

5. The water supply required for combined system (for partial automatic sprinkler and Fire Department hose) shall be calculated in accordance with (2) above plus an amount equal to the hydraulically calculated sprinkler demand or 550 litre per minute for light hazard occupancy groups or 1900 litre per minute for ordinary hazard occupancy groups.

6. The size of combined system shall be at least 150 mm or hydraulically designed to provided the required flow (5) and pressure.

7. The standpipe shall be located in noncombustible enclosure such that it will be able to provide hose stream to the most remote area of the floor served.

8. The hose shall be connected to the standpipe within 1.5 m from the floor. Hose stations shall be easily accessible for inspection and testing.

Table-3 : Piping for Standpipe System

Materials	Standard
Copper Tube	ASTM B75, ASTM B88
Copper and Copper-Alloy Tube	ASTM B251
Steel Pipe	ASTM A55, ASTM A120, ASTM A135
Wrought Steel or Iron	ANSI B36.10

Table-4 : Standpipe Fittings

Materials	Standard
Cast Iron	ANSI 616.1, ANSI B 16.4
Copper	ANSI B16.18, ANSI B16.22
Malleable Iron	ANSI B16.3
Steel	ANSI B16.5, ANSI B16.9, ANSI B16.11, ANSI B16.25, ASTM A234

Occupancy Classification

Every building or portion thereof shall be classified according to its use or the character of occupancy as a building of occupancy A, B, C, D, E, F, G, H, J or k as defined below:

Occupancy A : Residential

Occupancy B : Educational

Occupancy C : Institutional

Occupancy D : Health Care

Occupancy E : Assembly

Occupancy F : Business and Mercantile

Occupancy G : Industrial

Occupancy H : Storage

Occupancy J : Hazardous

Occupancy K : Miscellaneous

Minor occupancy incidental to operations in another type of occupancy shall be considered as part of the main occupancy, and shall be classified under the occupancy group relevant for the main occupancy.

Any occupancy not mentioned specifically shall be classified by the authority under the occupancy group to which is use most closely resembles, considering the potential life and fire hazard.

Each occupancy group shall be sub divided as detailed in the following sections. The example provided for each occupancy group are nonexhaustive and indicative only. If there is any use or character of occupancy in a building which is not mentioned here, it shall be classified by the authority.

Occuoancy A : Residential

Buildings classified under this occupancy shall include all buildings that provide sleeping and living accommodations to related or unrelated groups of people, with or without cooking or dining facilities, except any building classified under occupancy C or D. This occupancy shall be subdivided as follows:

A 1 Detached single family dwelling

These shall include any building, detached from neighboring buildings by distances required by this Code, and having independent access, which is used for private dwelling by members of a single family.

Occuoancy B : Educational

Building classified under this occupancy shall include all buildings in which education and care are provided to children and adults. This occupancy shall be subdivided as follows:

B 1 Educational facilities

These shall include any building or portion thereof used for purposes involving assembly for instruction, education and recreation of more than six persons, and which is not covered by occupancy E, for example school, college, university class rooms, lobbies and related facilities, coaching centers, tutorial homes etc.

Pile concreting

For bored or driven cast-in-situ piles, concrete shall be deposited in such a way as to preclude segregation. Concrete shall be deposited continuously until it is brought to the required level. The top surface shall be maintained as level as possible and the formation of seams shall be avoided.

For under-reamed piles, the slump of concrete shall range between 100 mm and 150 mm for concrete in water free holes.

For large diameter holes concrete may be placed by tremie or by drop between bucket; for small diameter boreholes a tremie shall be utilized.

A slump of 125 mm to 150 mm shall be maintained for concreting by tremie. In case of tremie concreting for piles of smaller diameter and length up to 10 m, the minimum cement content shall be 350 Kg /m³ of concrete. For larger diameter and /or deeper piles, the minimum cement content shall be 400 Kg /m³ of concrete.

Concrete to be used in bored or driven cast-in-situ piles shall have a strength greater than 20 Mpa and a minimum cement content of 400 Kg /m³. For such piles not exceeding a depth of 6 m, where underwater concreting is not involved and where soil conditions are favorable and nonaggressive, the concrete strength may be 15 Mpa with a minimum cement content of 350 Kg /m³, provided that a higher strength concrete is not needed from structural considerations.

For concreting under water, the concrete shall contain at least 10 percent more cement than that required for the same mix placed in the dry. The amount of coarse aggregate shall be not less than one and a half times, nor more than two times, that of the fine aggregate. The materials shall be so proportioned as to produce a concrete having a slump of not less than 100 mm, nor more than 150 mm, except where plasticizing admixtures is used in which case, the slump may be 175 mm.

Requirements for excavation and fills

Excavation for building foundation or for other purpose shall be done in a safe manner so that no danger to life and property prevails at any stage of the work or after completion.

Permanent excavation shall have retaining walls of sufficient strength made of steel, masonry, or reinforced concrete to retain the embankment, together with any surcharge load.

Excavation for any purpose shall not extend within 300 mm under any footing or foundation, unless such footing or foundation is first properly underpinned or protected against settlement.

Support to adjoining buildings and structures

Notice to adjoining property

Prior to any excavation close to an adjoining building in another property, a written notice shall be given to the owner of the adjoining property at least 10 days ahead of the date of excavation. The person undertaking the excavation shall, where necessary, incorporate adequate provisions and precautionary measures to ensure safety to the adjoining property and shall supply the details of such measures in the notice to the owner of the adjoining property. He shall obtain approval of the authority regarding the protective provisions, and permission of the owner of the adjoining property regarding the proposed excavation in writing.

Protective measure

The protective measures shall incorporate the following:

1) Where the level of the foundations of the adjoining structure is at or above the level of the bottom of the proposed excavation, the vertical load of the adjoining structure shall be supported by proper foundations, underpinning or other equivalent means.

2) Where the level of the foundations of the adjoining structure is below the level of the bottom of the proposed excavation, provision shall be made to support any increased vertical or lateral load on the existing adjoining structure caused by the new construction.

If on giving the required notice, incorporating or proposing to incorporate the protective provisions which have duly been approved by the authority, the owner of the adjoining property refuses to permit the proposed excavation or to allow necessary access and other facilities to the person undertaking the excavation for providing the necessary and approved protection to the adjoining property, the responsibility for any damage to the adjoining property due to the excavation shall be that of the owner of the adjoining property.

Excavation work

Every excavation shall be provided with safe means of ingress and exit kept available at al times. When an excavation has been completed, or partly completed and discontinued, abandoned or interrupted, or the permits have expired, the lot hall be filled graded to eliminated all steep slopes, holes, obstruction or similar sources of hazard. Fill materials shall consist of clean, noncombustible substances. The final surface shall be graded in such a manner as to drain the lot, eliminate pockets, prevent accumulation of water, and preclude any threat of the damage to the foundations on the premises or on the adjoining property.

Methods of protection

a) Shoring, bracing, and sheeting : with the exception of rock cuts, the sides of all excavations, including related or resulting embankments, 1.5 m or greater in depth or height measured the level of the adjacent ground surface to the deepest point of the excavation, shall be protected and maintained by shoring, bracing and sheeting, sheet piling or other retaining structures. Alternatively, excavated slopes may be inclined not steeper than 1:1, or stepped so the average slope is not steeper than 45 ⁰ with no step more than 1.5 m high, provided such slope does not endanger any structure, including subsurface structures. All sides or slopes of excavations of embankments shall be inspected after rainstorms, or any other hazard increasing event, and safe conditions shall be restored. Sheet piling and bracing needed in trench excavation shall have adequate strength to resist the possible forces resulting from earth and surcharge pressure.

Structural System Limitation

The following limitations shall be imposed on the use of some structural systems and configurations:

1) Vertical irregularities of structures

Type I : Stiffness irregularity (soft storey) :

A soft storey is one in which the lateral stiffness is less than 70 % of that in the storey above or less than 80% of the average stiffness of the three storey above.

Type II : Mass irregularity :

Mass irregularity shall be considered to exist where the effective mass of any storey is more than 150 % of the effective mass of an adjacent storey. A roof which is lighter than floor below need not be considered.

Type Ш : Vertical geometric irregularity :

Vertical geometric irregularity shall be considered to exist where horizontal dimension of the lateral force-resisting system in any storey is more than 130 % of that in an adjacent storey, one storey penthouse need not to be considered.

Type IV : In-plane discontinuity in vertical lateral force-resisting element:

An in-plane offset of the lateral load-resisting elements greater than the length of those elements.

Type V : Discontinuity in capacity (Weak storey):

A weak storey is one in which the storey strength is less than 80 % of that in the storey above. The storey strength is the total strength of all seismic-resisting elements shearing the storey shear for the direction under consideration.

2) Plan irregularities of structures

Type I : Torsional irregularity (to be considered when diaphragms are not flexible):

Torsional irregularity shall be considered to exit when the maximum storey drift, computed including accidental torsion, at one end of the structure transverse to an axis is more than 1.2 times the average of the storey drifts of the two ends of the structure.

Type II : Reentrant corners:

Plan configurations of a structure and its lateral force-resisting system contain reentrant corners, where both projections of the structures of the structure beyond reentrant corners are greater than 1.5 % of the plan dimension of the structure in the given direction.

Type Ш : Diaphragm discontinuity:

Diaphragm with a abrupt discontinuities or variations in stiffness, including those having cutout or open areas greater than 50 % of the gross enclosed area of the diaphragm, or changes in effective diaphragm stiffness of more than 50 % from one storey to next.

Type IV : Out-of-plane offsets:

Discontinuities in a lateral force path, such as out-of-plane offsets of the vertical elements.

Type V : Nonparallel system:

The vertical lateral load-resisting elements are not parallel to or symmetric about the major orthogonal axes of the lateral force-resisting system.