Durability Of Control High Performance Concrete: An Experimental Study

Abstract

The durability problems of Reinforced Cement Concrete Structures and the increasing use of concrete in exposure like sea water and acidic environment are making new demand on the material. This research Work intended to develop M70 grade control High Performance Concrete using Chemical Admixture only.M70 Grade control High Performance Concrete was Casted, Cured and Tested by Performing Experiments like Compression Test (150mm diameter and 300mm height cylinders),Ultrasonic Pulse Velocity Test& Flexural Strength Test(150mm??150mm??700mm size beams), Split Tensile Test(150mm diameter??300mm height cylinders), Sorptivity Test(100mm diameter,50mm thickness specimen), Sea water and Acid Attack Test(150mm??150mm??150mm size cubes), Accelerated corrosion Test(100mm diameter and 200mm height cylinder).The Results showed that M70 Grade Control High Performance Concrete Possess better Durability Properties and can be improve more by suitable addition of Mineral Admixture/Admixtures.

Keywords: Durability, Seawater; Sorptivity; Accelerated corrosion; Mineral Admixtures
List of Notation
ACI American Concrete Institute
CO2 Carbon Dioxide
IS Indian Standard
OPC Ordinary Portland Cement
GFRHPC Glass Fibre Reinforced High Performance Concrete
HCl Hydrochloric Acid
H2SO4 Sulfuric Acid
MgSO4 Magnesium Sulphate
Na2SO4 Sodium Sulphate
MgCl2 Magnesium Chloride
NH4Cl Ammonium Chloride
W/B water/binder ratio
W/C water/cement ratio
SiO2 Silicon Dioxide
CaO Calcium Oxide
MPa Mega Pascal
ASTM American Society for Testing and Materials
HPC High Performance Concrete

1 Introduction and literature review
A long service life of structural concrete is considered synonymous with durability. Since durability under one set of conditions does not necessarily mean durability under another, it is customary to include a general reference to the environment when defining durability. According to ACI Committee 201, durability of Portland cement concrete is defined as its ability to resist weathering action, chemical attack, abrasion, or any other process of deterioration; that is, durable concrete will retain its original form, quality, and serviceability when exposed to its environment. No material is inherently durable; as a result of environmental interactions the microstructure and, consequently, the properties of materials change with time. Due to unique mechanical properties, reinforced concrete has become the largest volume structural material in the world. Concrete, however, is a porous media and penetration of undesired substances can cause progressive damage to it. A material is assumed to reach the end of service life when its properties under given conditions of use have deteriorated to an extent that the continuing use of the material is ruled either unsafe or uneconomical. Concrete Durability has been extensively studied for more than a century, therefore the origin and the progress of all types of attack are now rather well known. Seawater is dangerous for both plain and reinforced concrete because of its high salt content (about 3.5%). Most seawaters are fairly uniform in chemical composition, which is characterized by the presence of about 3.5 percent soluble salts by weight. The ionic concentrations of Na+ and Cl' are the highest, typically 11,000 and 20,000 mg/liter, respectively. However, from the standpoint of aggressive action to cement hydration products, sufficient amounts of Mg2+ and SO4' are present, typically 1400 and 2700 mg/liter, respectively. The pH of seawater varies between 7.5 and 8.4, the average value in equilibrium with the atmospheric CO2 being 8.2. Under exceptional conditions (i.e., in sheltered bays and estuaries) pH values lower than 7.5 may be encountered; these are usually due to a higher concentration of dissolved CO2, which would make the seawater more aggressive to Portland cement concrete. Costal and Offshore Sea Structures are exposed to the simultaneous action of a number of physical and chemical deterioration processes, which provide an excellent opportunity to understand the complexity of concrete durability problems in practice. Oceans make up 80% of the surface of the earth, therefore a large number of structures are exposed to sea water either directly or indirectly(e.g. wind can spray upto a few miles inland from the coast).Concrete piers, decks, break waters and retaining walls are widely used in the construction of harbour and docks. The use of concrete drilling platforms and oil storage tanks is already on the increase. Concrete exposed to marine environment may deteriorate as a result of combined effect of chemical action of sea water constituents on cement hydration products, crystallization pressure of salts within concrete if one face of the structure is subjected to wetting and others to drying conditions and corrosion of embedded steel in reinforced concrete members. Attack on concrete due to any one of these causes tends to increase the permeability. Deterioration of concrete is also promoted when it is exposed to aggressive environments like balcony slab, parking garages, industrial plant structures etc. Embedded reinforcement and exposed concrete surface will suffer long term deterioration. The ability of concrete to resist weathering action, chemical attack or any process of deterioration is called durability of concrete.
Sulphate attack, Acid attack and corrosion of steel are common durability related problems in concrete and therefore in recent years more emphasis has been put on the durability issue of concrete. This is discussed in IS 456:2000, section8 (Sengupta A.K. et al.).When Concrete Structures are exposed to harmful chemicals that may be found in some ground water, industrial effluents and sea waters (Reddy M. et al.2012), then corrosion is the main cause of deterioration in concrete structures. Percentage decrease in compressive strength increases with the age of acid immersion. With the age of acid immersion percentage decrease in compressive strength increases and maximum percentage decrease in compressive strength is found at 90 days age of acid immersion (Sashidhar C. et al. 2010).Deterioration of concrete structures in marine environment is a phenomenon that involves understanding of different aspects (Sravana P. et al. 2011). The effect of an aggressive Chemical environment on concrete with ordinary Portland cement and silica fume either as a binary combination or a ternary combination with flyash was investigated (Goyal S. et al.2009) by using 1% sulphuric acid,1% hydrochloric acid and 1% nitric acid. Ternary mixes with OPC, silica fume and fly ash performed better than binary mixes containing only flyash. There is a strong interest in finding better ways of assessing the material properties of concretes which determine durability. The process of deterioration in concrete is largely by water. The sorptivity appears to be an especially useful property of this kind (Hall C. 1989). The 28 days cured binary blended concrete specimens were suffered moderate acid attack and the 90 days cured binary blended concrete were affected slightly by acid attack (Murthi P. et al.). Metakaolin based GFRHPC mixed concrete were exposed to 5% concentrated solutions of HCl, H2SO4, and MgSO4 for 30, 60 and 90 days and tested for compressive strength. Maximum loss of compressive strength occurred in case of H2So4 acid immersion in comparison with HCl and MgSo4 acids (Sudarsana Rao H. 2012).High Performance Concrete mixes prepared (Shannag et al. 2003) with W/B ratio = 0.35 containing various proportions of natural pozzolan (blend of certain volcanic stuff) (0%, 5%, 10%, 15% by weight of cement) and silica fume (0, 20, 40, 60 kg/m3) with naphthalene formaldehyde sulfonated superplasticizer and checked performance in severe sulphate environments (Na2SO4, MgSO4) and in Sea Waters. The investigation indicated that the concrete mix containing 15% natural pozzolan, and 15% silica fume showed the best protection in sulphates solutions and sea waters by retaining more than 65% of its Compressive strength after one year of storage. High Performance Concrete mixes containing fine ground ceramics as Portland cement replacement in an amount of upto 60% of mass were developed (Eva Vejmelkova et al. 2012). The compressive strength decreased very fast for the replacement levels higher than 20%; the produced concrete lost its high performance character. For same level water absorption coefficient was relatively low, the frost resistance was excellent and showed good chemical resistance in MgCl2, NH4Cl, Na2SO4, HCl environments. Quantitative assessment of different cement replacement levels with silica fume (0%, 2.5%, 5%, 7.5%, 10%, 12.5%, 15%) on strength and durability properties for M60 (W/B = 0.32), M70 (W/B = 0.3) and M110 (W/B = 0.232) grades of High Performance Concrete mixes was carried out (K. Perumal et al.2004). Replacement level of 10% with silica fume in M60, M70, and M110 grades of High Performance Concrete mixes was found to be the optimum level to obtain higher values of compressive strength (72.22 MPa, 82.46 MPa, 121.22 MPa), split tensile strength (6.10 MPa, 5.85 MPa, 8.45 MPa), flexural strength (8.3 MPa, 9.1 MPa, 8.45 MPa) and elastic modulus (35.1 GPa, 37.5 GPa, 44.4 GPa) & lower values of porosity (2.2%, 2.15%, 1.95%), sorptivity (0.0210 mm/min 0.5, 0.0205 mm/min0.5, 0.0104 mm/min0.5) and saturated water absorption (1.25%, 1.2%, 1.05%).
This research was performed to generate data on durability characteristic of control HPC so later on Value added high performance concrete can be developed by adding suitable mineral admixture which can overcome all durability related deficiencies of concrete.
2 Objectives

This research started with experimental studies conducted on cement, fine aggregate, coarse aggregate and superplasticizer in order to find their properties which were used in the production of durable structural concrete.
The results obtained for the properties of cement, aggregates and superplasticizer were noted and used for mix design of M70 grade control high performance concrete.
The objective was to adopt a low water-cement ratio (W/C) for making a low porosity, impermeable concrete to reduce the acid penetration and sea water attack from the environment into structural concrete.

3 Experimental Research
3.1 Materials Used
3.1.1 Cement
Ordinary Portland cement (SANGHI-53 Grade) Confirming standard (IS 12269 -1987) was used in present study with properties listed in Table 1.

Table1 Properties of OPC 53 grade SANGHI cement
Sr. No. Properties Results
1 Loss of Ignition 1.56
2 %SiO2 19.70
3 % CaO 63.44
4 Specific Gravity 3.15
5 % Normal Consistency 29.5
6 Specific Surface(m2/kg) 306
7 Initial Setting Time (minutes) 145
8 Final Setting Time (minutes) 185
9 Compressive Strength(MPa)
3days
7days
28days
37.5
48.5
63.0

3.1.2 Coarse Aggregate
Crushed angular aggregates confirming standard (IS 383-1987) with maximum size of 20mm and 10mm was used having bulk density of 1600 kg/m3.The specific gravity was found to be 2.81 as shown in Fig.1.

3.1.3 Fine Aggregate
River sand from local sources confirming standard (IS 383-1987) was used as fine aggregate. The fineness modulus and specific gravity and water absorption were found to be 2.64, 2.82 and 1.87% respectively as shown in Fig.2.

3.1.4 Water
Fresh potable water free from acid and organic substances was used for mixing and curing the concrete.
3.1.5 Superplasticizer
Super plasticizer (chemical admixture) based on Polycarboxylic technology 'AURAMIX 400 supplied by Fosroc Chemicals (India) limited conforming to standard (IS 9103-1999) as shown in Fig.3 with specifications given in Table 2 was used for the work.

Table 2 Properties of Chemical Admixture (AURAMIX 400)
Appearance pH Volumetric mass Chloride Content Solid Content
Light Yellow colour 6 1.09kg/litre Nil 33%

3.2 Marsh Cone Test
Marsh cones have been used for a while in different industrial sectors to appreciate the fluidity of different types of grout or mud, such as drilling muds in the petroleum industry, injection grouts in rocks or soils and injection grout in prestressed ducts (Aitcin P. C. 2004). The principle of the method consists in preparing a grout and measuring how long it takes for a certain volume of the grout to flow through a funnel having a given diameter. The cones that are used can have different geometrical features and the diameter of the funnel can range from 5 mm to 12.5 mm. The amount of water, cement and super plasticizer needed to prepare 1.2 litre of grout is calculated. The test shown in Fig.4 was performed at W/C ratio of 0.33 in order to test the cement and super plasticizer under conditions similar to those of the paste of a high performance concrete. 1.2 litre grout is poured into marsh cone duly closing the aperture with a finger. Start a stop watch and simultaneously remove the finger. Find out the time taken in seconds for 5 minute and 60 minute, for complete flow out of the grout.This curve shown in Fig.5 is composed of two lines having different slopes. The intersection of these two lines corresponds to what is called the 'saturation point'. This is the point at which, in the experimental conditions used for the measurement of the flow time, any increase in the dosage of the super plasticizer has no effect on the rheology of the grout. The super plasticizer dosage corresponding to this point is called the saturation dosage, and the flow time, the flow time for the saturation dosage.

Fig.3 Super plasticizer Fig.4 Marsh Cone Test

Fig.5 Marsh Cone Test Results
3.3 Mix Proportion
It must be admitted that up to the present time, progress in the field of high-performance concrete has been the fruit of an empirical approach rather than a fundamental and scientific one. As has often been the case in concrete technology, advances in practice have proceded thorough scientific investigations. High-performance concrete is prepared through a careful selection of each of its ingredients. It is very difficult to gain the last MPa of compressive strength of a particular concrete mixture, or the 1 hour workability to place it safely and uniformly in the field, but it is so easy to lose them. The performance and quality of each ingredient become critical at a certain point as the targeted strength increases, but there are some issues that are more critical than others. Certain issues have a much stronger impact on the economics of high-performance concrete, and determine whether or not it will be competitive not only against steel but also against usual concrete.
The Mix Proportion shown in Table 3 was made for a concrete with slump 140mm and M70 grade as per proposed method given by Mehta and Aitcin (Aitcin P. C. 2004). The method follows the same approach as ACI 211-1 Standard practice for Normal, Heavy Weight and Mass Concrete. It is a combination of empirical results and mathematical calculations based on the absolute volume method. The water contributed by the super plasticizer is considered as part of the mixing water. A flow chart of this method is presented in Fig.6.

Fig.6 Flow Chart of Mix Design Method

Table 3 Mix Design Detail
W/C
ratio Cement (kg) Fine Aggregate (kg) Coarse Aggregate(kg) Water (Litre) Superplasticizer(Litre)
20mm 10mm
0.33 470 750 675 450 155 15.70

3.4 Casting and curing
Mixing of ingredients were done according to specifications given in standard (IS-516 1959) by machine mixing. The concrete was filled into the moulds shown in Fig.7 in layers approximately 5cm deep and compacted by vibrator. The specimens were removed from mould after 24 hours and were kept submerged in curing tank. After curing for a period of 1, 3, 7, 14, 28, 56, and 91 days, specimens were taken out and dried before testing.

3.5 Testing
Specimens were tested to ascertain properties at 1, 3, 7, 14, 28, 56 and 91 days by performing following Tests.
3.5.1 Compression Test
Compression Test on cylinders of size 150 mm diameters and 300mm height shown in Fig.8 was conducted on the compression testing machine (Aimil, 2000kN capacity). The load on cube was applied at a rate 5.2kN/s upto the failure of specimen. Average compressive strength of three cubes was taken after 7 and 28 days curing.

3.5.2 Ultrasonic Pulse Velocity Test
Mix proportion used in making, compacting and curing of concrete is very important as they affect the density and modulus of elasticity of concrete. The ultrasonic pulse velocity of concrete is related to these. Concrete quality was checked as per specifications given in standard (IS1331,Part-1 1992).The ultrasonic pulse was produced by transducer which was held in contact with one surface of the concrete member of size 150mm??150mm??700mm. After travelling a known path length in the concrete, the pulse of vibration was converted into an electrical signal by the second transducer held in contact with the other surface of the concrete member and the transit time of the pulse was measured.
3.5.3 Flexural Test
Flexural test was performed on beams of size 150mm??150mm??700mm shown in Fig.9 by placing them in flexural testing machine and load was applied on the uppermost surface along two lines spaced 200mm apart. The load was increased until bean fails and maximum load applied was recorded to find flexural strength.

Fig.9 Flexural Test
3.5.4 Split Tensile Test
Split tensile test on cylinders of size 150mm diameter and 300mm height shown in Fig. 10 was conducted on the compression testing machine (Aimil,2000kN) as per specifications given in standard (IS 5816 1999).The load was applied at a rate of 1.8kN/s upto failure of specimen. Average Split Tensile Strength of 3 cylinders was taken after 1, 3, 7, 28, 56 and 91days.

3.5.6 Sorptivity Test
The sorptivity is an easily measured material property which characterizes the tendency of a porous material to absorb and transmit water by capillarity. Sorptivity was carried out in accordance with standard ( ASTM C1585- 05 2005) using concrete specimens 100mm in diameter and about 50mm thick as shown in Fig.11. After being cooled to room temperature, the oven-dried specimens were waxed on the side and covered on one end with a loose plastic sheet attached with masking tape to allow the entrapped air to escape from the concrete pores while at the same time preventing water loss by evaporation. After obtaining the initial mass, the test surface (i.e. uncovered end) of each sample was placed in water maintained at 3-5mm level above the top of the support throughout the duration of the test. After sealing the sides of specimen of size 100mm diameter and 50mm thickness by using epoxy paint, initial mass was measured. The sorptivity test was conducted over six hours and the cumulative change in mass at specific intervals was determined. For each mass determination, the test specimen was removed from water and the surface was cleaned with a dampened paper towel to remove water droplets. The mass of the sample was then measured and the sample was replaced to continue the test. The expression described in standard (ASTM C1585-04) was used to determine water absorption as a function of time. The cumulative absorption values were plotted against the square root of the times and sorptivity (the initial rate of water absorption) was obtained as the slope of the line that best fits the plot.

Fig.11 Sorptivity Test
3.5.7 Sea water and Acid immersion Test
The resistance of concrete to sea water and Acid attack was studied by determining variation in compressive strength of concrete cubes immersed in sea water and acid water having 5% of Hydrochloric Acid (HCl) by weight of water. The concrete cube specimens of size 150 mm were cast and after 28 days of water curing, the specimens were removed from the curing tank and allowed to dry. The weights of concrete cube specimen were taken. The acid attack test on concrete cube was conducted by immersing the cubes in the acid water for 28, 56 and 91 days after 28days of normal water curing. Hydrochloric acid (HCL) with pH of about 3 at 5% weight of water was added to water in which the concrete cubes were stored. The pH was maintained throughout the period. After immersion, the concrete cubes were taken out of sea water and acid water. Cubes after immersion in HCL are shown in Fig.12. Then, the specimens were tested for compressive strength. The resistance of concrete to acid attack and sea water attack was found by the % loss of weight of specimen and the % loss of compressive strength on immersing concrete cubes in acid water and sea water.

3.5.8 Accelerated Corrosion Test
Accelerated corrosion test shown in Fig 13 was performed by Galvanostatic method. A steel bar 25mm diameter and 200mm length was embedded in concrete cylinder which act as anode. The cylinder is immersed in 5% NaCl solution concentration and copper rod was used as cathode. The test specimen was impressed to a constant voltage of 60V from D.C. power for 6 hours. Then the cylinder was broken as shown in Fig.14 and steel bar was cleaned and weighted. Corrosion rate in mm per year was calculated as per standard (ASTM G1-90).

4 Test Results and Discussion
From a practical point of view, it is not worth while studying cement superplasticizer compatibility with a grout that is not too fluid or too thick, because most of the compatibility problems could be hidden. It has been found from experience that it is convenient to adjust the W/C ratio of the grout so that the 5 minute Marsh cone flow time is between 60 and 90 seconds. In any case, if the W/C ratio has to be raised to 0.33 to obtain a grout with a 5 minute flow time between 60 and 90 seconds, it is better to look for cement or another superplasticizer to make a high-performance concrete. The Results of Marsh Cone Test results shown in Fig.5 confirm that there is an optimum dosage of 1.2% by weight of cement for the plasticizer (AURAMIX 400) used.
Up to now, high-performance concrete has always been transported in the same way as usual concrete using transit truck mixers. However, it can also be transported with stationary trucks with or without agitators. The main problem faced during concrete transportation is slump loss.For fresh concrete slump obtained was 145mm.So the concrete mix Design is proper.
From Fig.15 and Table 4, 5 and 6, it can be seen that compressive strength of cylinders at 1, 3, 7, 28, 56 and 91 days obtained are 29.31MPa, 35.38MPa, 42.30MPa, 58.91MPa, 62.94MPa and 69.05MPa respectively. The increase in strength is about 63.24% at 91 days in comparison with 7 days. The compressive strength of high-performance concrete increases as the W/C ratio decreases. For a contractor an ideal concrete should stay plastic as long as needed for it to be placed easily, but as soon as it is placed it should harden within a few hours without developing any excessive heat, shrinkage or creep. The microstructure of high-performance concrete was more compact, including the transition zone with the coarse aggregate, resulting in a thin or no transition zone at all. Therefore, the mechanical properties of the coarse aggregate influenced some of the mechanical properties of high-performance concrete. Therefore, the sacrosanct W/C ratio law is no longer true in the case of some high-performance concretes made with 'weak' coarse aggregates. For any coarse aggregate there is a critical value of the W/C ratio below which any further decrease of the W/C ratio does not result in a significant increase of the compressive strength. This critical value depends on the strength of the rock from which the coarse aggregate is made, but also on the maximum size of the coarse aggregate. This is because when crushing a particular rock the smallest fragments are usually stronger than the coarsest because they contain less defects.
The knowledge of the modulus of elasticity of concrete is very important from a design point of view when the deformations of the different structural elements comprising the structure have to be calculated.Table 5and Table 6 indicates that the average secant modulus of elasticity values at 7, 28 and 56 days are 37.64GPa, 41.54GPa and 45.75Gpa respectively. The values are almost same at 28 and 56 days. The higher values confirm that the structural concrete is high performance.
From Flexural Test Results as shown in Fig.16 and Table 9 and 10, the flexural strength of beams at 7, 28, 56 and 91 days obtained are 4.77MPa, 6.93MPa, 7.34MPa and 7.4MPa respectively. The increase in strength at 91 days is about 55.14% in comparison with 7days. The failure surface showed that failure occurs at the weakest link that is coarse aggregate/ mortar interface.
Fig.17 and Table 11,12 and 13 shows that the split tensile strength of cylinders at 1, 3, 7, 28 ,56 and 91 days obtained are 1.81MPa, 2.08MPa, 2.78MPa, 3.67MPa, 3.81MPa and 3.90MPa respectively. The increase in strength at 91 days is about 40.29% in comparison with 7 days. The crushing strength of the coarse aggregate was mobilized when the failure occurred.
Fig.18 and Table 14 indicates that the sorptivity values at 28, 56 and 91 days obtained are 43??10-3mm/min0.5, 81??10-3 mm/min0.5 and 81??10-3 mm/min0.5 respectively. Lower values also confirm the good quality of structural concrete. The value remained almost same at 56 and 91 days and increases in comparison with 28 days because of presence of CaOH2 after hydration as no mineral admixture is added.
In a marine environment, chloride ion and sulfate ion penetrating into the concrete from sea water forms calcium chloroaluminate (Friedels Salt) and calcium sulphoaluminate (Ettringite). Both the products occupy a greater volume after crystallization in the pores of concrete than the compounds they replace. The formation of gypsum hydrate causes an increase in volume of concrete. Fig 19 and Table 15, 16 and 17 indicates that there is negligible increase in weight of cubes when immersed in Sea water for 28, 56 and 91 days respectively but compressive strength is decreased by 2.48%, 16.48 and 26.51% respectively. Concrete when exposed to seawater of different concentrations, possible cause for strength reduction is the formation of expansive as well as leachable compounds as concrete specimens were cured in seawater. Sea water entered into concrete and reacts with hydrated product of cement and slag formed ettringite or friedels salt. Due to these expansive materials, micro cracks were developed inside concrete and the bond between hydrated product and aggregate particles become weak. The concrete gradually became porous due to leaching action of the newly formed compounds. Thus, the concrete was deteriorated and loss in compressive strength of concrete was occurred.
When immersed in HCl solution, concrete was chemically exposed to the pH that produces a progressive neutralization of the alkaline nature of the cement paste, removing alkalies and dissolving portlandite (Ca OH)2) and C-S-H gel. The chloride (Cl-) dissolved in water speeds up the rate of the leaching of Ca(OH)2 transforming to CaCl2 which is very soluble, and thus increases the porosity and permeability of concrete leading to the loss of stiffness and strength. In the presence of Cl-, the release of calcium from Ca(OH)2 and C-S-H could be controlled by the precipitation of alteration solid phases. Fig 19 and Table 18,19 and 20 indicates that the decrease in weight of cubes when immersed in HCl solution for 28, 56 and 91 days were 1.24%, 1.48% and 1.64% respectively while compressive strength by 23.59%, 36.69% and 40.43% respectively. Since there was no additional admixture, further C-S-H gel was not formed which results into little impervious concrete and hence compressive strength reduced.
Corrosion of reinforcement steel in concrete is an electrochemical process where at the anode, iron is oxidized to iron ions and goes into solution and at the cathode oxygen is reduced to hydroxyl ions, thereby creating a short circuited corrosion cell between anode and cathode. Results shown in Fig.20 and Table 21,22 and 23 indicates that there was a loss in weight due to corrosion by 0.58%, 0.74% and 0.85% at 28, 56 and 91 days respectively and corrosion rate is 0.064mm/year, 0.08mm/year and 0.09mm/year at 28, 56 and 91days respectively. Therefore Use of chemical admixture along with good quality cement can produce concrete of any desired grade and if properly constructed, the service life of concrete structures can be enhanced by reducing corrosion rate and deciding proper reinforcement cover.
5. Conclusions
The following are the conclusions from the present study.
High early compressive strength indicates the obtained M70 grade control High Performance concrete is excellent as far as normal water curing is considered and it has also shown very good compressive strength at 28, 56 and 91days. 91 days strength is more than 1.17 times 28 days strength.
High modulus of elasticity is achieved at 28, 56 and 91 days and also Modulus of elasticity value confirms 5000'fck, which shows good quality of concrete.
High flexural strength is achieved at all ages and Flexural strength of control high performance concrete at 91days is around 1.06 times 28 days strength.
Pulse velocity at all ages is more than 4.3km/s from Non Destructive test which shows good quality of concrete.
Split tensile strength is more than 1/10 of expected compressive strength at all ages which indicates good casting quality of control High Performance concrete.
The Control High Performance concrete casted when exposed to HCl solution, the permeability increases as chloride (cl-) dissolved in water increases the leaching of Ca(OH)2 transforming to CaCl2. Because of this weight and compressive strength also decreases.
The porosity and strength of Control High Performance Concrete is reduced because of effect of chlorides and sulphates present in sea water.
High salt content increases portlandite and therefore porosity, which is harmful to reinforcement. Thus the protection of steel requires very compact concrete and adequate cover.
Sorptivity values are less at all ages which indicates that it has very low water absorbing capacity at all ages.
Accelerated corrosion results indicate that the control high performance concrete is very dense as the corrosion rate and weight in rod reduces less at all ages and hence has very good protection to steed with given cover.
From the research it is proposed that, to improve Strength and Durability of Control High Performance concrete which is made by Chemical Admixtures only, some mineral admixture/admixtures have to be added in making Concrete.

References
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Fig. 19 Acid and Sea Water immersion Test Results

Table 4 Compression Test Results at 1 and 3 days
Dimensions
(mm)
Date of casting Test Results at
1 day
Date of casting Test Results at
3 days
L D
Weight (kg) Failure
Load
(kN) Compressive
Strength
(MPa) Weight (kg) Failure
Load
(kN) Compressive
Strength
(MPa)
300 150 21/9/13 13.520 517.83 29.31 22/9/13 13.253 633.7 35.88

Table 5 Compression Test Results at 7 and 28 days
Dimensions
(mm)
Date of casting Test Results at 7 day
Date of casting Test Results at
28 days
L D
Weight (kg) Failure
Load
(kN) Compressive
Strength
(MPa) Weight (kg) Failure
Load
(kN) Compressive
Strength
(MPa) Secant modulus of Elasticity (GPa)
300 150 25/8/13 13.250 747.6 42.30 31/8/13 13.640 1040 58.91 37.64

Table 6 Compression Test Results at 56 and 91 days
Dimensions
(mm)
Date of casting Test Results at
56day
Date of casting Test Results at
91 days
L D
Weight (kg) Failure
Load
(kN) Compressive
Strength
(MPa) Secant modulus of Elasticity (GPa) Weight (kg) Failure
Load
(kN) Compressive
Strength
(MPa) Secant modulus of Elasticity (GPa)
300 150 31/8/13 13.623 1111.67 62.94 41.54 31/8/13 13.583 1219.67 69.05 45.75

Table 7 Ultrasonic Pulse Velocity Test Results at 28 and 56 days
Dimensions
(mm)
Date of casting Test Results at
28ay
Date of casting Test Results at
56 days
L B D
Weight (kg) Transit Time (??sec) Pulse Velocity (km/s) Concrete Quality Grading Weight (kg) Transit Time (??sec) Pulse Velocity (km/s) Concrete Quality Grading
700 150 150 25/8/13 40.467 162.33 4.31 Good 21/9/13 39.457 154.73 4.52 Excellent

Table 8 Ultrasonic Pulse Velocity Test Results at 91 days
Dimensions
(mm)
Date of casting Test Results at
91ay
L B D
Weight (kg) Transit Time (??sec) Pulse Velocity (km/s) Concrete Quality Grading
700 150 150 14/9/13 39.743 149.03 4.70 Excellent

Dimensions(mm)
Date of casting Test Results at 7 days
Date of casting Test Results at 28 days
L B D Weight (kg) Failure Load (kN) Flexural Strength (MPa) Weight (kg) Failure Load (kN) Flexural Strength (MPa)
700 150 150 25/8/13 39.477 26.83 4.77 21/9/13 40.467 39 6.93
Table 9 Flexural Strength Test Results at 7 and 28 days

Table 10 Flexural Strength Test Results 56 and 91 days
Dimensions(mm)
Date of casting Test Results at 56 days
Date of casting Test Results at 91 days
L B D Weight (kg) Failure Load (kN) Flexural Strength (MPa) Weight (kg) Failure Load (kN) Flexural Strength (MPa)
700 150 150 21/9/13 39.457 41.33 7.34 25/8/13 39.743 42.33 7.40

Table 11 Split Tensile Strength Test Results at 1 and 3 days
Dimensions (mm) Date of casting Test Results at 1 days Date of casting Test Results at 3 days
L D Weight (kg) Failure Load (kN) Tensile Strength (MPa) Weight (kg) Failure Load (kN) Tensile Strength (MPa)
300 150 21/9/13 13.070 127.87 1.810 22/9/13 13.080 147.17 2.08

Table 12 Split Tensile Strength Test Results at 7 and 28 days
Dimensions (mm) Date of casting Test Results at 7 days
Date of casting Test Results at 28 days
L D Weight (kg) Failure Load (kN) Tensile Strength (MPa) Weight (kg) Failure Load (kN) Tensile Strength (MPa)
300 150 25/8/13 12.997 196.33 2.78 31/8/13 13.337 259.5 3.67

Table 13 Split Tensile Strength Test Results at 56 and 91 days
Dimensions (mm)
Date of casting Test Results at 56 days
Date of casting Test Results at 91 days
L D Weight (kg) Failure Load (kN) Tensile Strength (MPa) Weight (kg) Failure Load (kN) Tensile Strength (MPa)
300 150 14/9/13 13.443 268.93 3.81 21/9/13 13.430 275.5 3.90

Table 14 Sorptivity Test Results

Dimensions(mm)
Date of casting Sorptivity (mm/min0.5)
Date of casting Sorptivity (mm/min0.5)
Thickness Diameter Test Results
at 28 days Test Results
at 56 days Test Results
at 91 days
50 100 22/9/13 0.043 0.081 14/9/13 0.080

Table 15 Immersion in Sea Water Test Results at 28 days
Dimensions(mm)
Date of casting Test Results at 28 days
L W T Weight (kg) % loss in weight Failure Load (kN) Compressive Strength (MPa) % loss in Strength
Before Immersion After Immersion
150 150 150 22/9/13 8.567 8.577 +0.12 1567.33 69.66 2.48

Table 16 Immersion in Sea Water Test Results at 56 days
Dimensions(mm)
Date of casting Test Results at 56 days
L W T Weight (kg) % loss in weight Failure Load (kN) Compressive Strength (MPa) % loss in Strength
Before Immersion After Immersion
150 150 150 22/9/13 8.547 8.563 +0.19 1387.33 61.66 16.48

Table 17 Immersion in Sea Water Test Results at 91 days
Dimensions(mm)
Date of casting Test Results at 91 days
L W T Weight (kg) % loss in weight Failure Load (kN) Compressive Strength (MPa) % loss in Strength
Before Immersion After Immersion
150 150 150 14/9/13 8.607 8.622 +0.17 1258.33 55.92 26.51

Table 18 Immersion in Acid Solution Test Results at 28 days
Dimensions(mm)
Date of casting Test Results at 28 days
L W T Weight (kg) % loss in weight Failure Load (kN) Compressive Strength (MPa) % loss in Strength
Before Immersion After Immersion
150 150 150 22/9/13 8.577 8.470 1.24 1253.67 54.72 23.59

Table 19 Immersion in Acid Solution Test Results at 56 days
Dimensions(mm)
Date of casting Test Results at 56 days
L W T Weight (kg) % loss in weight Failure Load (kN) Compressive Strength (MPa) % loss in Strength
Before Immersion After Immersion
150 150 150 22/9/13 8.550 8.423 1.48 1051.67 46.74 36.69

Table 20 Immersion in Acid Solution Test Results at 91 days
Dimensions(mm)
Date of casting Test Results at 91 days
L W T Weight (kg) % loss in weight Failure Load (kN) Compressive Strength (MPa) % loss in Strength
Before Immersion After Immersion
150 150 150 14/9/13 8.553 8.410 1.67 1020 45.33 40.43

Table 21 Accelerated Corrosion Test Results at 28 days
Dimensions(mm) Date of casting Test Results at 28 days Corrosion Rate in mm/year
Length Diameter Weight of the rod(gm) % loss in weight of rod
200 100 25/8/13 Before Corrosion After Corrosion
0.58
0.064
743.67 739.33

Dimensions(mm) Date of casting Test Results at 56 days Corrosion Rate in mm/year
Length Diameter Weight of the rod(gm) % loss in weight of rod
200 100 31/8/13 Before Corrosion After Corrosion
0.74
0.080
743 737.33
Table 22 Accelerated Corrosion Test Results at 56 days

Table 23 Accelerated Corrosion Test Results at 91 days
Dimensions(mm) Date of casting Test Results at 91 days Corrosion Rate in mm/year
Length Diameter Weight of the rod(gm) % loss in weight of rod
200 100 14/9/13 Before Corrosion After Corrosion
0.85
0.09
742 735.67

Source: Essay UK - http://www.essay.uk.com/free-essays/science/durability-control-high-performance-concrete.php



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