IMPROVE your CONCRETE SOLUTION

CONCRETE PROBLEMS AND SOLUTIONS

1. Common Problems

• Temperature increment due to hydration heat or chemical reaction of cement and water will cause crack.
• Temperature difference due to hydration heat of cement and surrounding air temperature will cause a strain that causes the crack.
• Concrete temperature increment is caused by the characteristics and temperature of the aggregate.
• The crack that is occured because of concrete temperature increment due to hardening process.
• Cracks in the concrete surface that is caused by concrete quickly dry out due to directly contact with surrounding air.
• Cracks because of failure formworks
• Formworks which is opened earlier will cause cracks due to inadequate concrete strength to hold its self weight.
• Fexural cracks because of over load distribution due to sructure function changing.
• Cracks caused by vibration in the concrete during hardening process due to disturbing concrete bonding process. Moreover, it causes weakness of  mortar and aggregate bonding and also concrete and reinforcement bonding which cause cracks along the reinforcement.
• Untidy formworks that causes bad concrete quality due to wasted pouring cement.
• Burned concrete structure more than 3000 degree celcius that can decrease the strength of reinforcement concrete, commonly caused by fire disaster.
• Weathering in the concrete surfaces that can decrease the strength of reinforcement concrete.
• Cracks or breaking concrete because of natural disasters.

2. Crack Paterns

• Flexural cracks; can not withstand bending moment, ussualy occured along the structure.
• Shear cracks; can not withstand shear forces, ussualy occured crosing the sections.
• Surfaces cracks; caused by quickly drying out.
• Cracks casued by can not withstand axial forces.
• Cracks casued by not binding reinforcement concrete.
• Forks cracking due to the concentration of reinforcement.
• Longitudinal cracks due to corrosion reinforcement.

3. Type of Failure Concrete

1. Porous concrete; caused by bad pouring concrete process, too coarse aggregate, inappropriate water cement factor, imperfect compaction due to too close reinforcement, wasted pouring cement etc.
2. Disintegration; commonly caused by natural corrosion process and life of time.
3. Cracks; mentioned above.
4. Spalling; commonly casued by fire disaster due to high temperature breaking the aggergate which contain silica. Commenced with small chunks thrown caused by high air presure in the concrete. Then, because of temperature increment, concrete surfaces will be fall of and weak and the strength of concrete will decrease.

4. Concrete Repairing Method

1. Chipping and Concreting;
   Fragile concrete is chipped to reach good concrete. For minor cracks, chipped as V form regularly and then washed with water using sprayer and/or brushes. Corrosion reinforcement shall be cleaned from contamination parts and adding new reinforcement for replacing the broken ones and welded on existing reinforcement.
   To make the existing and new concrete monolith, then douse it with concrete glues before concreting. Concrete quality shall be equal or higher than the existing. For V form on the minor cracks, can be filled by grouting material or mortar epoxy which can bind with concrete and steel well.
2. Grouting;
   Grouting injection is the best method for repairing the concrete on the hard location/position since the grouting material which is liquid relatively can fill the cracks area maximal. So, the binding of reinforcement and concrete will be renew and can be considered as masive concrete. Grouting injection presure shall be lower than allowable concrete tensille stress.
   There are 3 kinds of grouting material:
   1. Mortar Grouting; mixing of 1 cement : 2 sands : 1 water. Commonly use for large porous concretes.
   2. Cement Grouting; mixing of 1 cement : 1 water. Commonly use for small porous concrete and cracks.
   3. Chemical Grouting; consist of epoxy material which is liquid relatively that is conducted with injection.
3. Jacketing;
   Coating concrete surfaces wholly or separately. Commonly use for doty or distegrate concretes. Stages of jacketing is followed:
   a. chipp the doty concrete surfaces
   b. coat with concrete glues
   c. Pouring the concrete coating. Use Shotcrete for big area. For more than 5 cm thickness, use wiremesh to avoid cracks that is caused by shrinkage.
4. Strengthening
   Conducted to increaseing strength and daktail of the structure. Shall be planned and adequate technical requirements. There are kinds of stregthen that can be applied:
   a. increasing strength of reinforcement;
       add steel plates or tensile reinforcements.
   b. increasing strength of concrete;
       use jacketing and/or concreting method.
   c. increasing allowable strength of reinforcement concrete or increasing the section of structure;
      add bending and tensile reinforcement combined with jacketing and concreting method.
   d. Additional structure component;
      Add new shear walls, columns, beams and stiffner

Improve your Concrete Test Method

Existing Concrete Tests

Terms used in the implementation of the assignment based on the calculation procedure of Concrete Structures for Buildings / Tata cara Penghitungan Struktur Beton untuk Bangunan gedung (TCPS-BBG), SNI 03-2847, 1992.

1. Loading Test

Loading procedure

1. Initial reading of deflection, prior to loading implementation.
2. The amount of total load, including dead load has worked, is equivalent with 0.85 (1.2 DL + 1.0 LL).
3. Loading test is conducted shall not be less than 4 loading stages (load as much). The deflection shall be measured in every stage.
4. Read the deflection after 24 hours loading thereafter remove the load and measure the deflection.
5. Read the deflection 24 hours after the load was removed.

The structure adequate the technical requirements when:

1. Measured maximum deflection for ebam, slab and/or roof is less than L/20000 h.
2. If the deflection is more than L/20000 h, measured deflection after 24 hours load test is removed is at least 75% of maximum deflection for normal concrete or 80% for precast.
3. Retest for failure normal concrete can be conducted at least 72 hours after the load test is removed.

The tested structure adequate technical requirements if:

1. Retested structure is free from failure indication visually.
2. Recover deflection in the second test shall be at least 80% of maximum deflection.

2. Convermeter Test

The purpose is to identify the diameter, distance and quality of the reinforcement including concrete cover. This test is conducted with radiograph method that can identify the reinforcement condition directly and give the information of the reinforcement to identify reinforcement quality.

3. Corrosion Test

To identify corrosion rate of reinforcement. This test is conducted with supplying small electricity to the reinforcement in the large crack concrete area to identify the rate of corrosion with electricity potential difference.

4. Vibration Test

To identify Load Bearing of the tested structure including mode shapes values and natural frequency with damping factors. Vibration is given from ultra dynamic vibrator with sweap generator 5-1000 Hz that is connected with amplifier. Measurement is recorded by triaxial accelerometer or velocity transducer that is installed on that location.
Another advantage of this instrument is can identify Pile head stiffness, pile length, area of pile section, level of discontinuitas, possible range of stiffness from ground/pile conditions.

5. Shock Test

Purposes:

1. Identify the stiffness of beam and column and the integrity of beam and column.
2. Identify stiffness of pile head, length and section area of the pile.
3. Identify end of pile condition whether there is necking in the cast in situ pile or no.

Method:

1. Elastic pulse is given by 1 kg hammer punching to the tested structure.
2. Load transducer will receive the wave impact.
3. The signal from transducer ais saved in the micro computer.

Shock Test Instruments and tools:

1. Z-80A Zilog micro computer
2. Converter
3. Conditioning Electronics
4. Sensonic Vibration Transducer
5. Load Cell/Integral Torsional Accelerometer
6. Hammer 1 kg
7. Connecting Cable
8. Recording Device T-912
9. Tectronic scope with Ocilloscope camera Co. 212

This link below is only for your information. No advertisement purposed.....
http://www.mradcorp.com/prod_shocktesting.html
hopefully this link is usefull to little bit understanding about shocking test equipment.

So sorry for can't give you the instruments related with this tests in detail. Maybe someday I'll provide it including the estimation prices.

Have a nice Keeping Improve your Things....!!!