MAHARASHTRA INSTITUTE OF TECHNOLOGY, AURANGABAD.

A PRESENTATION ON

SHOTCRETE CONCRETE TECHNOLOGY

UNDER THE GUIDANCE OF ASST PROF. R.L.SIRALE Submitted bySINGH NITESH J. ROLL NO. 49

INTRODUCTIONShortcreting has proved to be the best method for

construction of curved surfaces.Domes are now much easier to construct with the

advent of shotcrete technology. Tunnel linings are also becoming easy with this technology.

Not only are these but there a wide range of applications where this technology has been a leading one.

This technical paper includes the concept of shotcrete and how it differs from conventional concrete.

It also enumerates the different types of process involved in shotcreting

DEFINITION OF SHOTCRETEShotcrete is a mortar or high performance concrete

conveyed through a hose and pneumatically projected at high velocity onto a backing surface.

It is the force of this spraying action that leads to compaction of the concrete or mortar which then forms layers of concrete to the required thickness.

Shotcreting has been an acceptable way of placing cementitious material in a variety of applications.

Usually patented polypropylene fibers are included in the shotcrete which increases the cohesive nature of the shotcrete through mechanically binding the cementitious materials together.

This mechanism reduces the rebound waste that occurs through the shotcreting process and these fibers also resist plastic shrinkage and cracking through their ability to enhance the early stage tensile strength of concrete.

SHOTCRETE VERSUS CONVENTIONAL CONCRETE

Unlike conventional concrete, which is first placed and then compacted in the second operation, shotcrete undergoes placement and compaction at the same time due to the force with which it is projected from the nozzle.

Shotcrete is more dense, homogeneous, strong, and waterproof than is possible to obtain by any other process.

Shotcrete is not placed or contained by forms. It can be impacted onto any type or shape of surface, including vertical or overhead areas.

It forms an excellent bond with the substrate and can be given a variety of surface finishes.

DRY PROCESSES

Simplified sketch of a typical dry mix shotcrete system

DRY PROCESS - AN OVERVIEW Working of dry process proceeds as per the

following steps:

Step1: Pre blended, dry or semi-dampened materials are placed into shotcrete equipment and metered into a hose.

Step2: Compressed air conveys materials at high velocity to the nozzle where the water is added.

Step3: Then the material is consolidated on receiving surface by high impact velocity.

The dry process can be used for any shotcreting applications from the smallest patching and sealing works to largest projects.

The maximum production achievable with dry process equipment ranges from 10-12 yards per hour of dry mix depending on the conditions.

To achieve ultimate capacity it is necessary to use 2”-2.5” hose and larger compressors.

Most applications have production rates of 2-6 cubic yards per hour of mix.

WET PROCESSES

One typical type of wet-mix shotcrete system

WET PROCESS - AN OVERVIEW Working of wet process proceeds as per the following

steps:

Step1: All ingredients, including water, are thoroughly mixed and introduced into the shotcrete equipment.

Step 2: Wet material is pumped to the nozzle where compressed air is introduced to provide high velocity for placement and consolidation of the material onto the receiving surface.

Step 3: Mostly wet-process shotcreting is done with premixed mortar or small aggregate concrete.

The mix design and consistency of supply are very important in order to provide a mix with the workability or plasticity to be pumped through a small-diameter hose.

Sand gradation is the same as for the dry process and for coarse aggregate mixes; 20-30 percent of 20mm aggregate is added. Cement content will vary according to the aggregate gradation and surface area.

However, most mixes contain approximately 700 pounds or more of cement.

NOVEL SHOTCRETE MATERIALS

POLYMER MODIFICATIONPOZZOLANIC ADMIXTURES FIBER REINFORCEMENTLOW VELOCITY SHOTCRETESTEEL FIBRE REINFORCED MICRO SILICA

SHOTCRETE

EQUIPMENTS USED IN SHOTCRETEBatching and mixing equipmentAdmixture dispensersAir compressorNozzles

APPLICATION OF SHOTCRETESupport of underground openings in tunnel, mines,

drainage adits and exploratory audits.Rock slope stabilization and support for excavated

foundations, often in conjuction with rock and soil anchor systems.

Channel linings, protection of bridge abutments and stabilization of debris-flow prone creeks.

Rehabilitation of reinforced concrete structures such as bridges ,chemical processing and handling plants.

Rehabilitation of deteriorated marine structures such as bulkheads, piers, sea wall and dry docks.

Shotcrete finds a major application in tunneling. Tunnel lining is made much easy by this process

Rehabilitation of subway tunnels

Shotcrete technology proved to be more efficient and easy for the construction of domed roofs

Domes

ADVANTAGESLittle or no framework is required.Cost effective method for placing concrete.Ideal for irregular surfaces application.Allows for easier material handling in areas with

difficult access.Easy start up, shutdown and clean up.An increase in load bearing capacity due to

redistribution of stresses.Excellent corrosion resistance.

DISADVANTAGESRain may wash out the cement leaving a sandy

surface, or it may saturate the shotcrete and cause sloughing or sagging

Strong wind will separate the material between the nozzle and the point of deposit, reducing the strength

It requires skilled and experienced labours.A greater degree of geotechnical knowledge is

requiredImproperly applied shotcrete may create conditions

much worse than the untreated condition

CONCLUSIONThe use of Shotcrete to build new concrete structures

as well as to restore and repair existing structures is well known and documented and it is perhaps the most diverse method available for concrete construction.

The use of this innovative technology is increasing day by day and procedures for its proper performance are well developed and high quality work is regularly obtained.

Shotcrete is a viable option for doing superstructure repair (unformed) and substructure repair (unformed) if done strictly according to specifications and best practices.

It is a good substitute for the manual lay-up method for vertical and overhead applications using rapid set mortar.

REFRENCESShotcrete in concrete restoration by Ivan Razal (Ph.D.,

P.Eng, Technical Director Gemite Products Inc.)Bieniawski Z.T. 1989. Engineering Rock Mass

Classifications. New York:Wiley. 251pages.Mahar, J.W., Parker, H.W. and Wuellner, W.W. 1975. Shotcrete

practice in under ground construction. US Dept. Transportation Report FRA-OR&D 75-90.Springfield, VA: Nat. Tech. Info. Service.

Morgan, D.R. 1993. Advances in shotcrete technology for support of underground openings in Canada. In Shotcrete for underground support V, proc. engineering foundation conf., Uppsala, (eds J.C. Sharp and T. Franzen), 35

Standard practice for shotcrete concrete (U.S.ARMY MANUAL)

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