New generation concrete for tall structures with PCEs and Beyond

• What is Concrete?

o C OMBINATION OF

o O RGANIC (SYNTHETIC) AND

o N ATURAL  INGREDIENTS 

o C ASTED AND CURED WITH OR WITHOUT

o R EINFORCEMENT IN THE

o E NVIRONMENT USING

o T ECHNOLOGY AND

o E FFECTIVE HUMAN RESOURCES.

• Factors affecting Concrete Quality
   
  • Influence of W/C on capillary porosity
  1. Effect of w/c on Porosity of hardened concrete
  2. Powers equation eq
       Vp=100w/c-36.15α 
     At identical degree of cement hydration α : Powers (1964); Oberholster ( 1986) and decreasing w/c, the result is a reduction in capillary porosity of the hardened cement paste (Vp)
  
  
  • Concrete for tall structures
  1. HIGH PERFORMANCE CONCRETE
  2. SELF COMPACTING CONCRETE
  3. SHRINKAGE COMPENSATED CONCRETE
  4. INTERNALY CURED CONCRETE
  5. HIGH STRENGTH CONCRETE
  6. FIBRE REINFORCED CONCRETE
  7. POLYMER MODIFIED CONCRETE
     
     
  • SELF COMPACTING CONCRETE
  Definition : A highly flowable, yet stable concrete that can spread readily into place and fill the formwork without any consolidation   and  without  undergoing  any   significant separation.
  
  
  • Benefits : 
  • Reduction in Construction Time. 
  • Reduction in construction costs. 
  • Improved working environment. 
  • Improvement in environmental loadings 
  • Improved concrete quality in difficult placement conditions. 
  • Improved surface quality.
  
  
  • Variables That Affect Self Compacting Concrete Proportions
  • Properties of mortar. 
  • The mortar will have a serious impact on the final result.   
  • The ratio of coarse aggregate in the whole mix. 
  • The use of super plasticizing admixtures, to improve fluidity and workability. 
  • The ratio of sand in the mortar will determine the degree of workability, as well as segregation resistance.
  • The quality and quantity of super plasticizers, will be the main factors that determine the flowability of the self compacting concrete.
  • Granulometry.
  
  
  •  Mix Proportion Design Methods for SCC
  1. The Rational Mix Design Method – Okamura and Ozawa (1995)
  • The coarse aggregate content is fixed at 50% of the solid volume of the concrete.
  • The fine aggregate content is fixed at 40% of the mortar volume.
  • The water/binder ratio is assumed to be 0.9 – 1.0 by volume depending on the properties of the binder(s).
  • The superplasticizer dosage and final water/binder ratio are determined so as to ensure self-compactability.
  
  
  2. Model for Self Compacting Concrete – Petersson et al. (1996)
  Designed in the field to meet the rigors and specifications of various construction projects. It includes stages, such as determining the void content, blocking criteria, mortar proportions and concrete proportions. All these criteria are fulfilled according to the requirements of the project in question, considering strength, durability and so on.
  
  
  3. Linear Optimization Mix Proportioning – Domone et al. (1999)
  Step 1: A typical air content is chosen (1 – 1.5% for non-air-entrained mixes).
  Step 2: The coarse aggregate content is fixed.
  Step 3: A binder composition is chosen using the guidelines in Table below or from past experience.
  
  
  
  
  
  
  
  
  
  Step 4: The maximum water / binder ratio is chosen to ensure that the following three conditions are satisfied.
  The paste has sufficient plastic viscosity (before addition of super plasticizer) to provide adequate segregation resistance. This is estimated by means of the specific gravity of the binder, retained water ratio (βP) and deformation coefficient (EP).
  The concrete has sufficient compressive strength using the generalization of Feret’s formula proposed by Sedran et al., (1996).
  The durability requirements are met.
  The minimum value of water / binder ratio from 1, 2 and 3 is chosen.
  Step 5: The volume of the sand in the mortar is chosen.
  Step 6: The paste content is calculated and adjusted if outside the limits.
  Step 7: The water and binder contents are calculated with the water being a limiting factor and set before Step 5 if greater that 200 kg/m³.         
  The above steps may be calculated using a simple spreadsheet which allows the use of linear optimization to obtain the best solution within the overall constraints of the mix design (Domone et al.; 1999). A target minimum paste content has been found to be effective as this may give rise to minimum cost mix as well as minimizing the effects of heat of hydration and shrinkage.
  Step 8: The super plasticizer dosage is then estimated from tests on the mortar component of the mix using the V-funnel test.
  Step 9: The concrete mix is then made and tested for fresh concrete properties.
  
  
  • List of test methods for workability properties of SCC
  
  

  Sr. No.	Method	Property
  1	Slump-flow by Abrams cone	Filling ability
  2	T50 cms lump-flow	Filling ability
  3	J-ring	Passing ability
  4	V-funnel	Filling ability
  5	V-funnel at T5 minutes	Segregation  resistance
  6	L-box	Passing ability
  7	U-box	Passing ability
  8	Fill-box	Passing ability
  9	GTM screen stability test	Segregation resistance
  10	Orimet	Filling ability

  
  
  
  
  
  
  •  High Performance Concrete
  ACI Definition :Concrete meeting special combinations of performance and uniformity requirements, that cannot always be achieved routinely using conventional constituents and normal mixing, placing, and curing practices.

  Benefits:

  • Ease of placement

  • Early age strength

  • Long-term mechanical properties

  • Permeability

  • Density

  • Heat of hydration

  • Volume stability

  • Long life in severe environments

   PCE And Future Generation Admixtures

  · LIGNOSULFONATES 

  · SNF AND SMF PCS, PCES AND OTHERS 

   

  · Why Change to PCE and Future Generation Admixtures

  IMPROVEMENT IN CONSTRUCTION TECHNIQUES.

  TIME LIMITS.

  INCREASING LOADS.

  COMPLICATED STRUCTURES.

  ENVIRONMENTAL CONCERNS.

  COMPLEX MIXES.

  AVAILABILTY CONCERNS

   

  · PCE