Thursday 17 November 2016

Strengthening of reinforced concrete beams using ultra high performance fibre reinforced concrete (UHPFRC)


Introduction

              A novel technique used to improve the performance of existing structural elements is the application of additional Ultra High Performance Fibre Reinforced Concrete (UHPFRC) layers or jackets in connection to the existing elements. The efficiency of this technique has not been adequately studied, and there are not any published studies on the evaluation of this method with comparisons to other traditional strengthening methods such as the use of Reinforced Concrete (RC) layers and jackets. The technique of strengthening using additional RC layers and jackets is one of the most commonly used techniques in seismic areas. There are several published experimental and theoretical studies on beams and columns strengthened with conventional concrete. A crucial parameter in this technique, which can considerably affect the durability and the performance of the strengthened structures, is the concrete shrinkage strain of the additional layers/jackets. Additional stresses are induced in strengthened elements, and cracking of the new layer and/or debonding may occur. The use of UHPFRC could potentially improve both durability and resistance due to its superior mechanical properties.

Reinforced concrete beams prior to strengthening: Numerical modelling and  experimental validation

            The Initial, prior to strengthening, Beam (IB) examined in this study is based on a previous experimental program. Initial beam’s cross sectional dimensions were 150 mm by 250 mm and the length was equal to 2200 mm. The reinforcement consisted of two bars with a diameter of 12 mm (2H12) made of steel with a characteristic yielding stress value of 500 MPa in the tensile side with a cover of 25 mm. The characteristic cylinder concrete compressive strength of the initial beam at 28 days was found equal to 39.5 MPa. The effective span was equal to 2000 mm and the beam was tested under a four-point bending loading with an imposed deflection rate of 0.008 mm/s. The distance between the two loading points in the middle of the span was equal to 500 mm. For the finite element analysis, ATENA software was used. Concrete was simulated with an eight-node element, with nonlinear behaviour and softening branches in both tension and compression using SBETA constitutive model. The ascending compressive branch of this model is based on the formula.




recommended by CEB-FIP model code 90, while its softening law is linearly descending from the peak stress until a limit compressive strain, which was defined by the plastic displacement and the band size, using the fictitious compression plane model. In tension, linear ascending branch and exponential softening branch based on the fracture energy needed to create a unit area of a stress free crack were used. In all the analyses smeared crack approach was used. For the simulation of steel bars, linear elements with bilinear behaviour were used. The numerical results (IBnum) are compared to the respective experimental for (IBexp) and the results are presented in. From the results presented in, very good agreement between the numerical and the respective experimental results was observed. The same assumptions were used for the modelling of RC layers and beams presented in the following sections.

3. Experimental investigation and numerical modelling of UHPFRC

3.1. UHPFRC material preparation
         UHPFRC is a material with enhanced strength in tension and compression and significantly high energy absorption in the post-cracking region. One of the main characteristics of UHPFRC is the enhanced homogeneity which is achieved by using fine aggregates only. In the mix design of the present study, silica sand with maximum particle size of 500 lm was used together with silica fume and Ground Granulated Blast Furnace Slag (GGBS). Silica fume, with particle size almost 100 times smaller than cement, improve not only the density of the matrix but also the rheological properties, while GGBS is used as a partial replacement of cement. High steel fibre content (3%) of straight fibres with 13 mm length and 0.16 mm diameter were used. The mix design is presented and it was based on a previous experimental investigation.
            For the preparation of UHPFRC the dry ingredients were mixed first for 3 min in a high shear mixer Zyklos (Pan Mixer ZZ 75 HE), then the water and the superplasticizer were added to the mix and, at the end, the steel fibres were added gradually. The specimens were cured in a steam curing tank at 90 _C for 3 days and the testing was conducted 14 days after casting. These curing conditions were found to be appropriate for the acceleration of the curing, since the strength achieved after 3 days in the steam curing tank was the same with the strength achieved 3 months under normal curing conditions.

3.2. Compressive and direct tensile tests and numerical modelling
           The standard cube compressive tests (100 mm side) were conducted and the mean compressive strength was found equal to 164 MPa while for the tensile strength, direct tensile tests of 6 dog-bone specimens were carried out.
           A constant loading rate of 0.007 mm/s was used to control the tests which is in agreement with the loading rate used by Hassan et al. leading to comparable results. The extension of the specimens was recorded using Linear Variable Differential Transformers (LVDTs). The setup of was used to measure the average extension over a gauge length of 105 mm, and the stress versus strain (extension normalized to the gauge length) results of all the 6 specimens together with the average curve are presented in.
          The experimental results indicate a variation of the tensile strength between 11.74 MPa and 14.20 MPa. An average stress– strain curve was calculated and the average strength was found equal to 12 MPa. The Young’s modulus was experimentally obtained from the slope of the initial linear part of the stress–strain graph in the linear part and a value of 57.5 GPa was calculated.
The setup used for the optical measurement of the crack together with the strain distribution at the moment when the first crack appeared, are presented in, alongside with stress– strain results for one of the examined specimens.
            Digital Image Correlation (DIC) system was used during the testing in order to monitor the crack opening and the strain distribution. According to these results, the strain is uniformly distributed along the specimen in the elastic part of the stress–strain distribution (strain values below 0.001). Then, in the second phase (strain between 0.001 and 0.005) there is a combination of micro cracks and elastic strain in the neck of the dog bone specimen and, in this phase, the multiple micro cracks opening was taken into account as an average crack opening along the monitoring length. For strain values higher than 0.005, all the extension of the specimen was due to the crack opening.





Fig. 5. Stress–strain results for the direct tensile tests



Fig. 4. Direct tensile tests 
(a)\geometry and (b) experimental setup.

3.3. Experimental and numerical investigation of UHPFRC layers under
flexural loading
               In this section, experimental and numerical results of layers with 50 mm depth were examined. During the casting process, the specimens were cast by pouring the material centrally along the long side and filling the first layer up to approximately 90% of the height of the specimen before the compaction by external vibrator. Afterwards, the moulds were filled and compacted as described in BS EN 14651:2005, and then the specimens were rotated over 90_ around their longitudinal axis for testing. Three identical specimens were tested under 4point loading, with 100 mm breadth, span length of 300 mm, and distance between the two loading points 100 mm. Two LVDTs were used to record the deflection of the layers in both sides, and the tests were conducted using a displacement control of 0.001 mm/s. An external yoke was used in order to exclude any additional displacement at the supports. The testing setup is presented in and a typical crack pattern is illustrated.

         The examined layers were modelled using the assumptions presented in Section 3.3. The numerical model is presented in, and the strain contours together with the crack pattern at midspan deflection equal to 10 mm, are presented in. A deflection equal to10 mm was selected as this was the typical mid-span deflection at the end of the tests.

             The examined layers were modelled using the assumptions resented in Section 3.3. The numerical model is presented in Fig. 11a, and the strain contours together with the crack pattern at midspan deflection equal to 10 mm, are presented in Fig. 11b. A deflection equal to 10 mm was selected as this was the typical mid-span deflection at the end of the tests (Fig. 10b).
            The strain localization in the middle of the span observed in the  experimental investigation (Fig. 10b) was in agreement with the numerical simulation’s results presented in Fig. 11b.
           The load deflection predictions are compared with the respective experimental results of all the three specimens [34] and the results are presented in Fig. 12.
           The numerical results are in good agreement with two of the examined layers, while in one of the examined specimens the strength was considerably lower compared to the other two. This could be attributed to local deficiencies due to the fibre distribution in the mix which resulted to a premature failure of the specimen.
           The assumptions presented in Section 2 and in Section 3.3, for the initial beam and the UHPFRC layers respectively, were used for the simulation of the strengthened beams with UHPFRC.

3.5. Experimental investigation of UHPFRC shrinkage
           In case of strengthened elements with concrete jackets, crucial parameters for the response of these ‘composite’ elements are the interface between the old and new concrete, and the shrinkage of the ‘new’ concrete [15]. Shrinkage strain measurements were recorded over the time for UHPFRC with 3% steel fibres and for Ultra High Performance Concrete (UHPC) without fibres. The mix design of Table 1 was used, and standard prisms 75 mm by 75 mmby 280 mmwere cast. The specimens were stored in a room with relative humidity 42% and temperature 20 _C (Fig. 13a) conditions similar to the standard climate (temperature 23 ± 2 _C and relative humidity or RH 50 ± 5) proposed by DIN 50014.
             The shrinkage strain distribution with the time is presented in Fig. 13b. As a starting point for these measurements (Day 0 in Fig. 13b), the third day after casting was used, when the initial curing was completed.
             The results presented in Fig. 13b indicate that the presence of the steel fibres considerably reduces shrinkage strain values and an average reduction of the shrinkage strain with the time of 30% was observed. In case of UHPFRC with 3% steel fibres (Table 1), the shrinkage strain 90 days after casting was measured equal to 565 microstrains. Shrinkage strain values are highly affected by a number of parameters including the mix design, the curing conditions and the geometry of the examined specimens. Yoo et al. used a special setup to simulate the conditions of free UHPFRC shrinkage effects on slabs and a very steep increase of shrinkage at the very early age was observed. Kamen and Kamen et al. Conducted measurements on specimens with similar geometry to those of the current study (prisms and dog-bone shaped specimens) and a distribution similar to the one presented in Fig. 13b was observed. Also, according to Kamen et al. In the first 2 days there is a chemical shrinkage state after the water–cement contact, followed by a swelling, and the main part of shrinkage strain is developed after the first two days.

5. Strengthening with additional RC layers. Comparisons of the two techniques
         In this section, the results of strengthened beams with UHPFRC are compared to respective experimental results of strengthened beams with traditional strengthening techniques using conventional concrete.
         The results of a previous experimental investigation were used. The geometry and the material properties of the initial, prior to the strengthening beam (IB), are presented in Section 2.
      Beams strengthened in the tensile side with RC layer were examined (ST_RCL_TS). In this case, strengthening was performed by adding a new concrete layer of 50 mm thickness in the tensile side with two bars with a diameter of 12 mm (2H12), made of steel with a characteristic yielding stress value of 500 MPa, and concrete cover of 25 mm (Fig. 23a). The 28 days characteristic cylinder concrete compressive strength of the layer was found equal to 39.5 MPa. The reinforcement of the layer was consisted of two bars with a diameter of 12 mm (2H12) with a total amount (volume) of steel exactly the same with the total volume of steel fibres used in
the layer of ST_UHPFR_TS with 3% steel fibres and 12 MPa average tensile strength.
         Beams strengthened in the compressive zone were also examined (ST_RCL_CS) and, in this case, plain concrete layer with 28 days characteristic cylinder compressive strength of 45.4 MPa, and 50 mm thickness was placed on the top of the beams (Fig. 23b). In this case, a loading rate of 0.008 mm/s was used. 
                                     


         This loading rate is equivalent to the one used for the testing of the prisms (0.001 mm/s) presented in Section 3.4. The distance between the load and the support in the full scale elements (750 mm) was almost 8 times higher compared to the respective
distance in the bending test of the prisms (100 mm) and a loading rate 8 times higher was used in order to obtain comparable results.
         The beams were tested under a four-point bending as described in Section 2 and the failure pattern is illustrated in Fig. 24a and b for specimens ST_RCL_TS and ST_RCL_CS respectively.
The load deflection results for specimens ST_RCL_TS and ST_RCL_CS together with the experimental results of the Initial Beam (IBexp) are presented in Fig. 25.
       From the results presented in Fig. 25, the moment at yield and failure for the strengthened specimens were calculated together with the respective increment, in comparison with the Initial Beam’s (IB) results of Table 3 (Table 4). In case of ST_RCL_TS, the yielding moment was defined by the yielding of the reinforcement of the additional layer, which occurs before the yielding of the reinforcement of the initial beam.
       These results were compared to the respective values calculated for the beams strengthened with UHPFRC with 12 MPa ultimate tensile strength, and the comparisons of My and Mu for the various techniques are presented in Fig. 26a and b.
         The results of Fig. 26 indicate that very high moment increments were observed for beams strengthened with an additional RC layer in the tensile side (ST_RCL_TS), since increments of 150% and 97% were observed for My and Mu. The respective increments for specimens strengthened with UHPFRC in the tensile side (ST_UHPFRC_TS) were found to be lower and equal to 29% and 31%. The results of Fig. 26 indicate that the highest moment increment was observed for a three side UHPFRC jacket and this was found equal to 167% and 178% for My and Mu respectively.
         In case of beams strengthened in the compressive zone, application of UHPFRC (ST_UHPFRC_CS) resulted to an increment of 19% and 28% for My and Mu, while the respective increment was slightly lower (25% for My and 22% for Mu) when normal concrete was used (ST_RCL_CS).
      The technique of strengthening in the tensile side with combination of UHPFRC layer and two steel bars was also examined. The same geometry and reinforcement with the one presented in Fig. 23a was used with the only difference that instead of normal concrete, UHPFRC with 12 MPa ultimate tensile stress was used (ST_UHPFRC_TS_12 MPa and steel bars). The load deflection results were compared to the respective results of ST_RCL_TS and with the initial, prior to strengthening, beam (IB) (Fig. 27).
       The results presented in Fig. 27 indicate that the initial stiffness and the ultimate load capacity were increased when conventional concrete was replaced by UHPFRC in reinforced concrete layers applied to the tensile side. The increment of the yield and ultimate bending moment values are presented in Table 5.
      The results of Table 5 indicate that there is an increment of 7% in the yield bending moment and 9% in the ultimate bending moment when the normal concrete of the layer is replaced by UHPFRC. The results indicate that even if the performance is overall enhanced, the contribution of the UHPFRC in this case was not fundamental.

6. Conclusions

        In this study, extensive experimental and numerical investigation was conducted to investigate the efficiency of UHPFRC for the strengthening of existing beams. Mechanical testing and shrinkage strain measurements were conducted in order to determine UHPFRC material properties, and these results were used for the numerical modelling. The following two conclusions were drawn regarding the behaviour of UHPFRC in tension and regarding the shrinkage strain.
1.The proposed stress–strain model in tension, which was consisted of an initial linear elastic part and a tri-linear post elastic behaviour can accurately predict the response of UHPFRC.
2.Shrinkage strain measurements were also presented for UHPFRC with 3% steel fibres and without steel fibres. The shrinkage strain was 30% reduced in case of UHPFRC with 3% steel fibres, compared to the respective measurements of plain UHPC.

            Extensive numerical modelling was conducted on beams strengthened with UHPFRC. Strengthened beams with additional layer in the compressive, in the tensile side, and with a three side jacket were examined. A parametric study with different values of UHPFRC tensile strength was also conducted and the following observations were made.


1.As expected, in case of specimens strengthened with UHPFRC in the compressive side, increment of the tensile strength of UHPFRC was not considerably affecting the response of the strengthened specimens. Ultimate moment increment less than 4% was observed when UHPFRC tensile strength was increased from 8 MPa to 16 MPa.
2.In case of strengthened specimens with UHPFRC in the tensile side, the ultimate moment was increased by 31% when UHPFRC tensile strength was increased from 8 MPa to 16 MPa.
3.The respective increment for strengthened specimens with three side jackets (ST_UHPFRC_3SJ) was significantly higher and equal to 53%.

           The effect of the post-peak (softening) stress–strain behaviour of UHPFRC on the overall performance of the strengthened beams was also investigated.
1.As expected, for beams strengthened in the compressive side, the effect of the post-peak behaviour of the tensile stress–strain model was negligible.
2.In case of beams strengthened in the tensile layer with UHPFRC layer, when the stresses in the post-peak branch were increased by 50%, the ultimate strength and moment were increased by 8%, while, when 50% lower stresses were used, the ultimate load and moment were reduced by 11%.
3.In case of beams strengthened with a three side jacket the respective ultimate strength increment was 2%, for 50% higher post-peak stresses, while reduction equal to 3% was observed for stress–strain model with 50% lower post-peak stresses.

      Sensitivity analysis was also conducted for the examined strengthened with UHPFRC beams, using different shrinkage strain values for UHPFRC. The main conclusion of this study was that in this case the response of the strengthened elements was not affected considerably by variations in the shrinkage strain value of UHPFRC.
Critical comparisons of this novel technique with the traditional method of strengthening with RC layers were also conducted and the following conclusions regarding the efficiency of the two techniques were drawn.
1.The highest moment increment was observed for a three side UHPFRC jacket and this was found to be equal to 167% and 178%, for My and Mu respectively. When three side jacket was used, the slip at the interface was considerably reduced, compared to the respective values of beams strengthened in the compressive or tensile side.
2.The increment in case of specimens strengthened with UHPFRC in the tensile side was found equal to 29% and 31% for My and Mu. Considerably higher increment was observed in case of beams strengthened with an additional RC layer in the tensile side (150% increment of My and 97% increment of Mu).
3.In case of beams strengthened in the compressive zone, the addition of UHPFRC resulted to an increment of My and Mu 29% and 28% respectively, while the increment was slightly lower (25% for My and 22% for Mu) when normal concrete was used, which indicates that there is no need for high strength concretes when strengthening in the compressive zone.

       For beams strengthened in the tensile side, combination of steel bars and UHPFRC was also investigated and an increment of 7% in the yield bending moment and 9% in the ultimate bending moment was observed, compared to the respective values of beam strengthened with RC layers. The results indicate that even if the performance is overall enhanced, the contribution of the UHPFRC in this case was not fundamental.

The main conclusion of this study is that superior performance can be achieved by the use of three sides UHPFRC jackets. In practise, UHPFRC could be used following the same procedure with the one used for RC jackets. The application of UHPFRC could be done using formworks by adapting the rheological properties of UHPFRC [26]. This novel technique has a great potential for the structural upgrade of the existing structures.



Reference

1.http://fulltext.study/preview/pdf/265998.pdf



Monday 14 November 2016

Process Of Manufacture Of Cement With Flowchart

PORTLAND CEMENT

Cement

          Cement is a material with adhesive and cohesive properties which make it capable of bonding minerals fragments into a compact whole.

        For constructional purposes, the meaning of the term "cement" is restricted to the bonding materials used with stones, sand, bricks, building stones, etc.

        The cements of interest in the making of concrete have the property of setting and hardening under water by virtue of a chemical reaction with it and are, therefore, called hydraulic cement.

         The name "Portland cement" given originally due to the resemblance of the color and quality of the hardened cement to Portland stone – Portland island in England.

Manufacture of Portland cement


Raw materials 

• Calcareous material – such as limestone or chalk, as a source of lime (CaO).
• Clayey material –        such as clay or shale (soft clayey stones), as a source of silica and alumina.

Methods of cement manufacturing

1. Wet process : Grinding and mixing of the raw materials in the existence of water.
2. Dry process : Grinding and mixing of the raw materials in their dry state.

The process to be chosen, depend on the nature of the used raw materials:

1. Wet process : The percentage of the moisture in the raw materials is high.

2. Dry process :
• The raw materials is so hard (solid) that they do not disintegrate by water
• Cold countries, because the water might freeze in the mixture
• Shortage of the water needed for mixing process.

1. Wet process

1. When chalk is used, it is finely broken up and dispersed in water in a washmill. The clay is also broken up and mixed with water, usually in a similar washmill. The two mixtures are now pumped so as to mix in predetermined proportions and pass through a series of screens. The resulting – cement slurry – flows into storage tanks.

2. When limestone is used, it has to be blasted, then crushed, usually in two progressively smaller crushers (initial and secondary crushers), and then fed into a ball mill with the clay dispersed in water. The resultant slurry is pumped into storage tanks. From here onwards, the process is the same regardless of the original nature of the raw materials.

3. The slurry is a liquid of creamy consistency, with water content of between 35 and 50%, and only a small fraction of material – about 2% - larger than a 90 µm (sieve No. 170).

4. The slurry mix mechanically in the storage tanks, and the sedimentation of the suspended solids being prevented by bubbling by compressed air pumped from bottom of the tanks.

5. The slurry analyze chemically to check the achievement of the required chemical composition, and if necessary changing the mix constituents to attain the required chemical composition.

6. Finally, the slurry with the desired lime content passes into the rotary kiln. This is a large, refractory-lined steel cylinder, up to 8 m in diameter, sometimes as long as 230 m, which is slightly inclined to the horizontal.

7. The slurry is fed in at the upper end while pulverized coal (oil or natural gas also might be used as a fuel) is blown in by an air blast at the lower end of the kiln, where the temperature reaches about 1450P o PC.

8. The slurry, in its movement down the kiln, encounters a progressively higher temperature. At first, the water is driven off and COR 2R is liberated; further on, the dry material undergoes a series of chemical reactions until finally, in the hottest part of the kiln, some 20 to 30% of the material becomes liquid, and lime, silica and alumina recombine. The mass then fuses into balls, 3 to 25 mm in diameter, known as clinker. The clinker drops into coolers. 

2. Dry process 

         The raw materials are crushed and fed in the correct proportions into a grinding mill, where they are dried and reduced in size to a fine powder. The dry powder, called raw meal, is then pumped to a blending silo, and final adjustment is now made in the proportions of the materials required for the manufacture of cement. To obtain a uniform mixture, the raw meal is blended in the silo, usually by means of compressed air.

      The blended meal is sieved and fed into a rotating dish called a granulator, water weighing about 12% of the meal being added at the same time. In this manner, hard pellets about 15 mm in diameter are formed.

          The pellets are baked hard in a pre-heating grate by means of hot gases from the kiln. The pellets then enter the kiln, and subsequence operations are the same as in the wet process of manufacture.

Grinding of the clinker 

    
     The cool clinker (produced by wet or dry process), which is characteristically black and hard, is interground with gypsum CaSOR 4R.2HR 2RO in order to prevent flash setting of the cement, and to facilitate the grinding process. The grinding is done in a ball mill. The cement discharged by the mill is passed through a separator, fine particles being removed to the storage silo by an air current, while the coarser particles are passed through the mill once again.

REFERENCE:
1.http://www.uotechnology.edu.iq

Saturday 12 November 2016

Types Of Concrete

Types Of Concrete 


1.Normal Concrete
          The concrete in which common ingredients of aggregate, water, cement are used is known as normal concrete. It is also called normal weight concrete or normal strength concrete.It has a setting time of 30 - 90 minutes depending upon moisture in atmosphere, fineness of cement and other properties of concrete.The development of the strength starts after 7 days the common strength values is 10 MPa to 40 MPa. At about 28 days 75 - 80% and almost at 90 days 95% of the strength is achieved of the total strength is attained.

Properties of Normal Concrete
1. Its slump varies from 1 - 4 inches.
2. Density ranges from 140 pcf to 175 pcf.
3. It is strong in compression and weak in tension.
4. Air content 1 - 2 %.
5. Normal concrete is not durable against severe conditions.
6. Compressive strength : 20 - 40 MPa (3000 - 6000 psi).
7. Flexural strength : 3 - 5 MPa (400 - 700 psi).
8.Tensile strength : 2 - 5 MPa (300 - 700 psi).
9. Modulus of elasticity : 14000 - 41000 MPa (2 - 6 x 106 psi).


2. Light weight concrete (LWC)
         The LWC defined as a type of concrete which includes an expanding agent in that it increases the volume of the mixture while giving additional qualities such as nailbility and lessened the dead weight.The density of normal concrete is of the order of 2200 to 2600. This self weight will make it to some extend an uneconomical structural material.Whereas the Self weight of light weight concrete varies from 300 to 1850 kg/m3. Porous light weight aggregate of low specific gravity is used in this concrete. such as pumice, scoria and most volcanic origin and artificial aggregate such as expanded blast furnace slag, vermiculite and clinker aggregates are used.

Properties of LWC
1. Density of light weight concrete is 240 kg/m³ (15pcf) -1850 kg/m³ (115 pcf).
2. Strength of light weight concrete blocks varies from 7 MPa (1000 psi) - 40 MPa (5800 psi).
3. Some times Air Entrained Admixtures are also added to it giving resistance to freezing and thawing along with strength.

Advantages of LWC
1. It helps reduce the dead load, increase the progress of building and lowers the hauling and handling cost.
2. The weight of building on foundation is an important factor in the design , particularly in case of weak soil and tall structures. The wall and floor are made of light weight concrete it will result in considerable economy.
3. Light weight concrete have low thermal conductivity.
4. Only method for making concrete light by inclusion of air. 
This is achieved by 
a) replacing original mineral aggregate by light weight aggregate
b) By introducing gas or air bubble in mortar
c) By omitting sand fraction from concrete. 
This is called no – fine concrete.
5. Light weight concrete aggregate exhibit high fire resistance.
6. Structural lightweight aggregate’s cellular structure provides internal curing through water entrainment which is especially beneficial for high-performance concrete.
7. Lightweight aggregate has better thermal properties, better fire ratings, reduced shrinkage, excellent freezing and thawing durability, improved contact between aggregate and cement matrix, less micro-cracking as a result of better elastic compatibility, more blast resistant, and has better shock and sound absorption, High-Performance lightweight aggregate concrete also has less cracking.
8. Improved skid resistance and is readily placed by the concrete pumping method 
a) Aerated concrete is made by introducing air or gas into a slurry composed of Portland cement.
b) No fine concrete is made up of only coarse aggregate , cement and water.These type of concrete is used for load bearing cast in situ external walls for building. They are also used for temporary structures because of low initial cost and can be reused as aggregate.


3. High density concrete (HDC)
           High density concrete is a concrete having a density in the range of 6000 to 6400 kg/cu.m. High density concrete is also known as Heavy weight concrete. High density concrete is mainly used for the purpose of radiation shielding, for counterweights and other uses where high density is required. Heavyweight concrete uses heavy natural aggregates such as barites or magnetite or manufactured aggregates such as iron or lead shot. The density achieved will depend on the type of aggregate used. Typically using barites the density will be in the region of 3,500kg/m3, which is 45% greater than that of normal concrete, while with magnetite the density will be 3,900kg/m3, or 60% greater than normal concrete. Very heavy concretes can be achieved with iron or lead shot as aggregate, is 5,900kg/m3 and 8,900kg/m3 respectively. Most of the aggregate specific gravity is more than 3.5.

Advantages of HDC
1.They are mainly used in the construction of radiation shields (medical or nuclear). Offshore, heavyweight concrete is used for ballasting for pipelines and similar structures
2.The ideal property of normal and high density concrete are high modulus of elasticity , low thermal expansion , and creep deformation. Because of high density of concrete there will be tendency for segregation. To avoid this pre placed aggregate method of concreting is adopted.
3.High Modulus of Elasticity, Low thermal Expansion ,Low elasticity and creep deformation are ideal properties.
4.The high density. Concrete is used in construction of radiation shields. They are effective and economic construction material for permanent shielding purpose.

4. Ready-mix Concrete (RMC)
       Ready-mix concrete has cement, aggregates, water   and   other   ingredients,   which are weigh-batched   at a   centrally located   plant. This is   then  delivered   to the   construction site in truck mounted transit mixers and can be used straight away without any further treatment.Ready Mixed Concrete, or RMC as it is popularly called, refers to concrete that is specifically manufactured for delivery to the customer’s construction site in a freshly mixed and plastic or unhardened state. Concrete itself is a mixture of Portland cement, water and aggregates comprising sand and gravel or crushed stone. In traditional work sites, each of these materials is procured separately and mixed in specified proportions at site to make concrete. Ready Mixed Concrete is bought and sold by volume – usually expressed in cubic meters. Ready Mixed Concrete is manufactured under computer-controlled operations and transported and placed at site using sophisticated equipment and methods. RMC assures its customers numerous benefits.

Advantages of RMC
1.   A centralized concrete batching plant can serve a wide area.
2.   Better quality concrete is produced
3.   Elimination of storage space for basic materials at site.
4.   Elimination of procurement / hiring of plant and machinery
5.   Wastage of basic materials is avoided
6.   Labor associated with production of concrete is eliminated
7.   Time required is greatly reduced
8.   Noise and dust pollution at site is reduced
        
5. Pozzocrete
          Unfortunately, adding extra water and fine aggregate leads to a weaker concrete. The usual remedies for this are either to increase the cement content, which is costly, or to use chemical admixtures, which can also be costly and may lead to segregation in marginal mixes. There is another and far more effective alternative.

Advantages of including of POZZOCRETE in concrete mixes to be pumped
1.Particle Size. 
Pozzocrete meets IS 3812 Specification with 66% passing the 325 (45-micron) sieve and these fine particles are ideal for void filling.  Just a small deficiency in the mix fines can often prevent successful pumping.
2.Particle Shape. 
Microscopic examination shows most Pozzocrete particles are spherical and act like miniature ball bearings aiding the movement of the concrete by reducing frictional losses in the pump and pining.  Studies have shown that Pozzocrete can be twice as effective as cement in improving workability and, therefore, improve pumping characteristics.

Pozzolanic Activity
        This chemical reaction combines the Pozzocrete particles with the calcium hydroxide liberated through the hydration of cement to form additional cementitious compounds which increase concrete strength.

Sand/Coarse Aggregate Ratio
       In pumped mixes, the inclusion of liberal quantities of coarse aggregate can be very beneficial because it reduces the total aggregate surface area, thereby increasing the effectiveness of the available cementitious paste.  This approach is in keeping with the “minimum voids, minimum area” proportioning method.  As aggregate size increases, so does the optimum quantity of coarse aggregate.  Unfortunately, this process is frequently reversed in pump mixes, and sand would be substituted for coarse aggregate to make pumping easier.  When that happens, there is a need to increase costly cementitious material to compensate for strength loss.  However, if Pozzocrete is utilized, its unique workability and pump ability properties permit a better balance of sand to coarse aggregate resulting in a more economical, pump able concrete.

6. Shotcrete
       Shotcrete is a process where concrete is projected or "shot" under pressure using a feeder or "gun" onto a surface to form structural shapes including walls, floors, and roofs. The surface can be wood, steel, polystyrene, or any other surface that concrete can be projected onto. The surface can be trowelled smooth while the concrete is still wet.

Advantages
1. Shotcrete has high strength.
2. Durability.
3. Low permeability.
4. Excellent bond and limitless shape possibilities.
5. The hardened properties of shotcrete are similar to conventional cast-in-place concrete.
6. The nature of the placement process provides additional benefits.
7. Excellent bond with most substrates and instant or rapid capabilities.
8. Particularly on complex forms or shapes. Addition to building homes, shotcrete can also be used to build pools.

REFERENCES

1.   http://theconstructor.org/concrete/types-of-concrete/966/
2.   http://www.aboutcivil.org/types-of-concrete.html
3.   google wikipedia