MICRO CONCRETE

MICRO CONCRETE

Micro-concrete is generally used as a repair material which is of non shrinking type. The application areas include:

Repair of damaged reinforced concrete elements like beams, columns, wall, etc. where access is restricted and compaction is not possible. 
For jacketing of RCC columns to increase load-taking capacity (strengthening of a vertical members)
Microconcrete is combination of cement, high quality graded fine aggregate, shrinkage compensating agents and dispersion agents in powder form marketed as dry powder in packets by construction chemical companies. This is to be mixed with predetermined amount of water depending on the consistency sought – trowelable or pourable. Applied as repair mortar or to fill the crevices which cannot be done by conventional concrete.

Micro concrete is a dry ready mix cementitious based composition formulated mainly for used in repairs works when the concrete is damaged and the area is restricted in movement due to which there is problem in placing concrete. Micro concrete is in dry powder from added with clean water on the site and its a good quality cement.

Renderoc constructive solutions ® RG Spl 

General purpose, non-shrink, cementitious micro-concrete

Uses

 Renderoc RG Spl is used for repairs to damaged reinforced concrete elements, particularly where access is restricted and where vibration of the placed material is diffi cult or impossible.

 It is suitable for various structural strengthening measures such as encasement build-ups, jacketing , piletop encapsulation resin system, etc. 

Advantages

  Gaseous expansion system compensates for shrinkage and settlement in the plastic state. 

 Can be pumped or poured into restricted locations. 

 Fluidity to allow for placement without vibration.

  Pre-bagged to overcome site-batched variations.

  Rapid strength gain to facilitate early reinstatement.

  High ultimate strengths and low permeability of cured repair.

  Contains no chloride admixture. 

 Ensures piletop integrity as part of a waterproofing system

Description 

Renderoc RG Spl is supplied as a ready to use blend of dry powders which requires only the site addition of clean water to produce a free-fl owing non-shrink repair micro concrete. The material is based on Portland cements, graded aggregates and fillers, and additives which impart controlled expansion characteristics in the plastic state, while minimising water demand. The low water requirement ensures high early strength and long-term durability.

 For larger repairs, the mixed Renderoc RG Spl may be modified by the addition of 5mm to 12mm clean, graded, saturated surface dry aggregates at site.

Design criteria

 Renderoc RG Spl can be applied in sections upto 100mm deep. For larger sections, the addition of approved aggregates may be required. This will depend on the specific configuration of the repair location. 

Properties 

The following results were obtained at a water:Powder ratio of 0.15 @ 300C. 

Test                                Typical result at 300C

 Compressive strength (N/mm2 )

 1 Day                                    30

 7 Days                                  60 

28 Days                                 75

 Flexural strength                   8N/mm2 @ 28 days 

Young’s Modulus                    25 kN/mm2

 Thermal conductivity             1.5 W/m0C 

 Fresh wet density                  2300 - 2400 kg/m3 

 Specification clauses

 Performance specification

 The fluid micro-concrete repair material shall be Renderoc RG Spl, a single component, cement based, micro-concrete to which only the site-addition of clean water ( and approved graded coarse aggregates where specified) shall be permitted. The micro-concrete shall contain no metallic aggregates, or chlorides and shall be shrinkage compensated in the plastic state. The micro concrete in the flowable consistency should achieve a compressive strength of not less than 30N/mm2 after 24 hours at 300C. Most importantly, the cured microconcrete shall have a coeffi cient of thermal expansion similar to that of the host concrete.

Application instructions

Preparation 

The unrestrained surface area of the repair must be kept to a minimum. The formwork should include drainage outlets for pre-soaking and, if beneath a soffi t, provision for airventing. Provision must also be made for suitable access points to pour or pump the mixed micro-concrete in place

Defective concrete surfaces must be cut back to a sound base. Smooth surfaces should be mechanically roughened. Corroded reinforcing steel should be exposed around its full circumference and cleaned to remove all loose scale and corrosion deposits. It is important to clean the steel to a bright condition. Grit-blasting is recommended. One coat of Nitozinc Primer should be applied on the reinforcing steel. If any discontinuity in the applied fi lm is noticed, one more coat has to be applied. Several hours prior to placing, the concrete substrates should be saturated with clean water. Immediately prior to placing, any free water should be removed. 

Mixing 

Care should be taken to ensure that Renderoc RG Spl is thoroughly mixed in a forced-action mixer of adequate capacity. Alternatively, mix in a suitably sized drum with a high torque (400/500 rpm) rotary drill fitted with a mixing paddle. It is essential that machine mixing capacity and labour availability is adequate to enable the placing operation to be carried out continuously. The quantity water required will generally be between 3.50 litres and 3.75 litres per 25 kg bag of Renderoc RG Spl. The optimum water content should be determined and accurately measured into the mixer. However it should not exceed 3.75 litres/25 kg in any case. With the mixer running, slowly empty Renderoc RG Spl bag into the mixer. Mix continuously for 5 minutes, ensuring a smooth even consistency of the mix. Where the addition of graded coarse aggregate has been specified it should be added after the water and Renderoc RG Spl are properly mixed. Mixing should then continue for a further 1 minute to ensure proper dispersion.

Form Work 

Slurry tight form work that will not deform or leak when subjected to hydraulic pressure imposed by the micro concrete will be fabricated and erected where the material is gravity fed, provision in the formwork will be made for a suitable feedhopper at the highest point. Where necessary, provision will be made for airvents to prevent air entrapment. Form work will be coated with Reebol mould releasing agent prior to fixing.

Placing 

The mixed material should be placed immediately. if placed by pump, standard concrete pumping practice should be followed. The pump and pipeline must be primed with cement slurry. Pumping should be commenced immediately after priming. If poured in the form work, avoid air entrapment by pouring from one side only. 

Curing 

As Renderoc RG Spl is a cement-based repair material, it should be cured immediately after stripping the formwork in accordance with good concrete practice. the use of Nitobond AR or any of Fosroc’s Concure range of curing compounds, sprayed on the surface of the Renderoc RG Spl. in a continuation fi lm, is recommended soon after tripping the form work. In harsh drying conditions, supplementary curing such a wed hessian or/or polythene sheeting must be used. 

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