TB-1703 — CONCERA® CP1028 Technical Bulletin

Rheology Modifying Water Reducer

Introduction

CONCERA® CP1028 is a patent pending rheology modifying polycarboxylate based ASTM C494 Type A water reducer that enables the production of Control Flow Concrete, a highly flowable concrete with minimal or no segregation using unmodified conventional mix designs. Control Flow Concrete’s typically have slump flow values in the 16-25" (406 to 635 mm) range and may require minimal external energy to properly consolidate. CONCERA® CP1028 is a component of GCP’s Control Flow Concrete System and is typically used in mix designs that also contain a PC based mid or high range water reducer. CONCERA® CP1028 imparts many desirable properties to Control Flow Concrete including segregation resistance, stability, improved passing and filling ability, excellent tolerance to moisture variation and extended slump life. CONCERA® CP1028 also produces concrete with consistent, predictable slump flow and air control properties and readily enables jobsite concrete to be retempered with water to restore slump lost during transit. CONCERA® CP1028 has minimal impact on other concrete properties including early and later age compressive strength and drying shrinkage, while initial time of set and total bleed may slightly increase.

ASTM C 1611-Standard Test Method for Slump Flow of Self-Consolidating Concrete (SCC) details a qualitative visual test procedure for measuring rheology, stability and segregation resistance properties of highly flowable concrete and SCC. The test procedure includes a visual inspection of the concrete spread after the slump flow test is completed. This inspection includes observing the distribution of coarse aggregate within the concrete spread and mortar fraction and bleeding characteristics around the perimeter of the spread. Finally, a Visual Stability Index (VSI) value is assigned to the concrete spread using 0-3 criteria as detailed to the right.

Visual Stability Index Values

  • 0 = HIGHLY STABLE - No evidence of segregation or bleeding.
  • 1 = STABLE - No evidence of segregation and slight bleeding observed as a sheen on the concrete mass.
  • 2 = UNSTABLE - A slight mortar halo ≤ 0.5 in. (≤ 10 mm) and/or aggregate pile in the center of the concrete mass.
  • 3 = HIGHLY UNSTABLE - Clearly segregating by evidence of a large mortar halo ≥ 0.5 in. (≥ 10 mm) and/or a large aggregate pile in the center of the concrete mass.

A CONCERA® CP1028 field test evaluation program using an array of 3500-6500 psi (24.2-44.8 Mpa) mix designs containing different types and quantities of cements, pozzolans and fine and coarse aggregates was conducted at several test sites in North America. The mix design and admixture test matrix included:

  • Conventional 8" (203 mm) slump using polycarboxylate based HRWR
  • Highly flowable 16-25" (406 to 635 mm) slump flow using polycarboxylate based HRWR
  • Control Flow Concrete 16-25" (406 to 635 mm) slump flow using CONCERA® CP1028 rheology modifying water reducer and polycarboxylate based HRWR

Table 1 above details summary of test results including initial slump flow, VSI, plastic air, initial time of set, early, 7, 28 day compressive strength along with 60 minute slump flow and VSI. Field test results clearly show CONCERA® CP1028 produces highly flowable, stable, segregation resistant concrete with excellent slump retention properties over 60 minutes and minimal impact on other pertinent plastic and hardened concrete properties.

Figure 1 below further details polycarboxylate based HRWR (black) and CONCERA® CP1028 (red) concretes VSI values over a range of slump flows. CONCERA® CP1028 concretes also typically contain a PC based MRWR or HRWR. CONCERA® CP1028 concretes consistently show better (lower) VSI values when compared to highly flowable PC based HRWR concrete with all VSI‘s < 1. Note: ACI 237-Self Consolidating Concrete document states – A VSI rating <1 is an indication that the highly flowable concrete is stable. ACI 237 further states that VSI ratings are subjective and should be used primarily as a quality control tool, rather than as a acceptance/rejection criteria for a specific mix design.

 

When CONCERA® CP1028 is incorporated into a conventional "off the shelf" mix design, and additional incremental improvements to the overall rheology, segregation resistance, stability or other properties are desired, relatively minor and inexpensive mix design modifications can be made. First, most conventional MRWR/HRWR mix designs are designed in the 5-8" (127- 203 mm) slump range and CONCERA® CP1028 has built-in water reducer capability to increase 5+ inch (127 mm) slump concretes up to the highly flowable 16-25" (406 to 635 mm) range. Therefore, since most CONCERA® CP1028 mix designs already contain a PC based MRWR or HRWR, rheology improvements can be realized by slightly reducing the PC based MRWR/HRWR dosage rate and increasing the CONCERA® CP1028 dosage rate. This adjustment will increase the total amount of rheology modifier in the concrete. Several other mix design adjustments are detailed below, with implications related to making a specific adjustment detailed in parentheses. It is highly recommended CONCERA® CP1028 Control Flow Concrete be tested prior to job startup using applicable mix designs and materials.

  • Adjust MRWR/HRWR – CONCERA® CP1028 ratio
  • Reduce total coarse aggregate content (increases drying shrinkage)
  • Reduce nominal coarse aggregate size (increases drying shrinkage)
  • Optimize coarse aggregate particle shape/angularity
  • Optimize coarse aggregate gradation, avoid severely gap graded coarse aggregate
  • Increase fine agg, reduce coarse agg content (water demand and shrinkage impact)
  • Increase mortar and/or paste fraction (water demand and shrinkage impact)
  • Slightly increase total cementitious content
  • Incorporate or increase the percentage of fly ash in the mix design
  • Reduce slump flow to low end of 16-25" (406 to 635 mm) range (workability impact)
  • Slightly increase plastic air content (strength impact)
  • Slightly reduce water content, increase CONCERA® CP1028 dosage rate

In summary, a widespread North America based field test program confirmed CONCERA® CP1028 enables the production of 16-25" (406 to 635 mm) Control Flow Concrete with minimal or no segregation using typically unmodified conventional mix designs. CONCERA® CP1028 imparts many other desirable properties to Control Flow Concrete including improved passing and filling ability, tolerance to moisture variation, consistent slump flow and slump flow retention properties and minimal impact on compressive strength and set time. Several minor mix design modifications can also be tested and implemented if additional improvements to overall rheology, stability and segregation resistance properties are desired

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Last Updated: 2018-11-29

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