3/5/2014. Disclaimer and Waiver of Liability. Portland Cement Association. Learning Objectives. Why do concrete problems occur?

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1 Disclaimer and Waiver of Liability T-20 Troubleshooting Concrete Mix Designs and Specifications Michelle L. Wilson, FACI Director, Education Portland Cement Association Tuesday, March 4, 2014 This document is for informational purposes only and is not to be construed as explicit engineering advice, or professional engineering services. This service is provided on the terms and understanding that the author(s) or companies represented by the CONEXPO-CON/AGG 2014 or author(s) makes no warranty, guarantee, or promise, express or implied, concerning the content or accuracy of the material herein and accessible via this service. No person or business entity should rely on the sole contents of this document to make any decisions. The CONEXPO-CON/AGG 2014 or author(s) or the companies that they represent are not responsible for the results of any actions taken on the basis of information in this service, nor for the actions of persons using this document, nor for any error in or omission contained in this document. The CONEXPO-CON/AGG 2014 or author(s) or any represented company expressly disclaims all and any liability and responsibility to any person in respect of anything, and of the consequences of anything, done or omitted to be done by any such person in reliance, whether wholly or partially, upon the whole or any part of the contents of this document Learning Objectives 1. Describe the general purpose of ASTM C94, Standard Specification for Ready Mixed Concrete and how it is applied in Concrete Specifications. 2. Introduce ACI , Specifications for Structural Concrete and how it is applied into contract documents. 3. Define common confusion in current specifications and note how we can troubleshoot existing specifications to ensure concrete meets final performance criteria. Portland Cement Association Founded in 1916 Headquarters: Washington D.C. Labs: Skokie, Illinois Mission: To improve and extend the uses of portland cement and concrete Why do concrete problems occur? Avoiding Problems Design- Constructability Design Mix Design Materials Selection Placement Procedures Environment GOAL Workmanship Environment

2 Concrete Mixtures Goals for Designing Concrete Mixtures Determine the most economical and practical combination Use readily available materials Produce a concrete that satisfies the performance requirements under particular conditions of use Fresh Concrete Properties Consistency Workability Uniformity Bleeding Setting & Hardening Hardened Concrete Properties Hydration rate and setting time Strength and durability Permeability and water tightness Volume Stability and Crack Control Aesthetics Need for Innovation Concrete Codes and Specifications ACI 318 Building Code Requirements for Structural Concrete ACI 301 Specifications for Structural Concrete ASTM C94 Standard Specification for Ready- Mixed Concrete

3 Confusion in Current Concrete Specifications Prescription vs. Performance w/cm vs. Strength Min. Cement Content Cement Type Slump vs. Quality Temp. Limit vs. Thermal Control Durability Requirements Curing Regime Acceptance Criteria Concrete Mix Design Summary of Absolute Volume Method ACI Strength Requirements 2. Determining W/CM 7. Cement Content 8. Cement Type 3. Coarse Aggregates 9. Admixture Effects 4. Air Content 10. Sand Requirements 5. Workability 11. Moisture Corrections 6. Water Content 12. Trial Mixes Basis for Proportioning Make Concrete Good ASTM C94 Sec 6 Option A - Performance Option B - Prescriptive Option C - Combined Performance Based Specifications w/cm vs. Strength Strength ACI Air Void Spacing/ Durability Factor Permeability/ Coulombs Shrinkage Tolerance Required design strength f cr (psi) W/CM Non-Air Entrained Air-Entrained Material Acceptability- ASR, Sulfate Testing

4 The Water-Cement Ratio Law Optimum Water-Cementitious Materials Ratio For given materials the strength of the concrete (so long as we have a plastic mix) depends solely on the relative quantity of water as compared with the cement, regardless of mix or size and grading of aggregate. Duff A. Abrams May, 1918 From Hover Minimum Cementitious Content General recommendations (PCA/ACI): For workability, finishability, and durability in flatwork follow recommendations in table: Max. Aggregate, mm (in) Min Cement, kg/m 3 (lb/yd 3 ) 37.5 (1½) 280 (470) 25 (1) 310 (520) 20 (¾) 320 (540) 12.5 (½) 350 (590) 10 (3/8) 360 (610) Types of Cement ASTM C150 (AASHTO M 85) ASTM C595 (AASHTO M 240) ASTM C

5 Workability Requirements Slump vs. Concrete Quality ACI Concrete construction 211.1: Reinforced foundation walls and footings Plain footings, caissons, and substructure walls Slump, mm (in.) Maximum Minimum 75 (3) 25 (1) 75 (3) 25 (1) Slump should be based on placement conditions not as an indication of concrete quality. Beams and reinforced walls 100 (4) 25 (1) Building columns 100 (4) 25 (1) Pavements and slabs 75 (3) 25 (1) Mass concrete 75 (3) 25 (1) On-site Water Addition? ASTM C94 Sec states, Water is allowed to be added on site if: Slump is less than desired Max water content is not exceeded Water add. takes no more than 15 min (can be multiple additions of water) Provided that no concrete has been discharged except for slump or slump flow testing 30 drum revolutions are added Temperature Limit vs. Thermal Control Thermal Control

6 Durability Considerations Resistance to Abrasion Abrasion Reactive Aggregates ASR Freeze/Thaw Chemical Attack Sulfates Seawater Exposure Corrosion Aggregate type Strength Finishing Curing Testing (ASTM C779 and C944) Resistance to Alkali Silica Reactivity Pozzolans, Slag, and Blended Cement Low Alkali Portland Cement Limit Concrete Alkalies Lithium Aggregate Selection and Beneficiation Resistance to Alkali-Silica Reactivity ASR Prism Test- ASTM C1293 < 0.04% expansion (1 year) Mortar Bar Test- ASTM C1260 < 0.10% expansion (14 days) Use of SCMs ASTM C1567 < 0.10% expansion (14 days) Caution: Limiting the alkali level of cement (<0.6%) may not be enough to mitigate ASR- focus must be on TOTAL alkalies in concrete ACI 318 Exposure Conditions ACI 318 Exposure Conditions

7 Resistance to Freeze-Thaw Total Air Content- ACI 318 Criteria : The aggregate is frost-resistant Sufficient strength is attained prior to first freezing (> 35MP 3.5 MPa or 500 psi) Sufficient strength is attained prior to cyclic freezing & thawing (> 31 MPa or 4500 psi) Adequate Air Void System ACI 318 Strength & w/cm Requirements for Freeze-Thaw Resistance ACI 318 Limits on Supplementary Cementing Materials for Resistance to Deicer Scaling ACI Resistance to Sulfates ACI 318 Strength and w/cm Requirements for Sulfate Resistance Low w/cm Type of Cement (lower aluminate) Use of Pozzolans, Slag, and Blended Cement Expansion Tests (ASTM C1012) Moderate- Class 1 < 0.10% at 6 months Severe- Class 2 < 0.05% at 6 months < 0.10% at 12 months Very Severe- Class 3 < 0.10% at 18 months See ACI 318 for definition of exposure classes * Note- PCA Requirements include a w/cm < 0.40, and a minimum compressive strength of 35Mpa (5000psi) for Very Severe (S3) Sulfate Exposure

8 Resistance to Corrosion Low w/cm 7 days Moist Cure Use of SCM s Proper Cover Depth Epoxy Coated Reinforcement Sacrificial Anode Cathodic Protection Surface Treatments ACI 318 Strength and w/cm Requirements and Chloride Limits for Corrosion Resistance Maximum water-soluble chloride ion expressed as a mass percentage of the cementitious material content Low-Permeability Concrete - Corrosion Resistance Cracking vs. Durability Permeability- ASTM C1202 Less than 2000 Coulombs Effect of test age? Volume Stability- Low Shrinkage Concrete Curing Regime Minimize water content Aggregate selection Top size, expansion Testing (ASTM C157) When not otherwise specified (ACI 301): Concrete shall be maintained above 50 F and in a moist condition for at least the first 7 days after placement. High-early strength concrete shall be maintained above 50 F and in a moist condition for at least the first 3 days

9 QA/QC Preconstruction meeting (proactive) Prequalification of finishing crew (proactive) Test panels, Mock ups Acceptance Criteria General Acceptance criteria -Architecturally acceptable concrete surfaces should be aesthetically compatible with minimal color and texture variations and minimal surface defects when viewed at a distance of approximately 20 ft (6m) or more as agreed upon by architect, owner, and contractor, or as otherwise specified. Acceptance Criteria (on-site) FRESH Temperature (ASTM C1064) Air content (ASTM C231 and C173) Workability (ASTM C143) HARDENED Strength (ASTM C31 and C39) Acceptance Criteria (Fresh Concrete) ASTM C94, Sec states, If the measured slump or air content, or both is greater than the specified upper limit, a check test shall be made immediately on a new test sample. In the event the check test fails, the concrete shall be considered to have failed the requirements of the specification. Acceptance Criteria (Fresh Concrete) ASTM C94, Sec states, If the measured slump or air content, or both is less than the lower limit, permit adjustments and obtain a new sample. If the sample of the adjusted concrete fails, s,a check test shall be made immediately on a new sample of the adjusted concrete

10 Acceptance Criteria (Hardened Concrete) ASTM C94, Sec 18.1 states, When strength is used as a basis for acceptance of concrete, standard specimens shall be made in accordance to Practice C31/C31M. Acceptance Criteria (Hardened Concrete) ASTM C31, Sec states, Immediately after molding and finishing, the specimens shall be stored for a period up to 48h in a temperature range from 60 and 80 F [16 and 27 C] and in an environment preventing moisture loss from the specimens

11 Acceptance Criteria (Hardened Concrete) ACI d Provide space, source of power and facilities to be used on the project for initial curing of concrete test specimens as required by ASTM C31/C31M for the sole use of the Owner s quality assurance testing agency ACI d Provide space and source of electrical power on the project site for initial curing of concrete test specimens as required by ASTM C31/C31M for the sole use of the Owner s quality assurance testing agency

12 Responsibility- Owner and Testing Agency ACI Curing of strength test specimens Initial curing Owner or Owner s representative will provide and maintain adequate facilities on the project site for initial storage and curing of the concrete specimens, unless otherwise specified. Specimens shall be stored under conditions that meet the requirements of ASTM C31 and shall be verified by Testing Agency. Such storage shall have temperature controls to maintain ASTM C31 temperature requirements. Calibrated temperature recording devices shall be used to record daily maximum and minimum temperatures of the initial curing environment Responsibility- Owner and Testing Agency ACI Curing of strength test specimens Transportation Testing Agency will recover and transport concrete specimens in accordance with ASTM C Final curing Final curing of strength test specimens shall be done in accordance with ASTM C31 and C511 until time of test. Be Clear on Desired Outcome Specify enough and the right hoops to jump through to get the performance you require for service conditions State the Obvious If it isn t in the Specification, it probably won t happen. Ex: Curing Regime Thermal Control Caution Requirements that Bind Contractors Hands Means and Methods Materials Types, Limits

13 Default vs. Optional Requirements Questions and Further Information There is more than one way to get the job done. Michelle L. Wilson, FACI Director, Education Portland Cement Association phone