Test Results
C-GRID is manufactured in a continuous fashion that enables the spacing between longitudinal strands and transverse strands to be varied depending on the product requirements. In addition, the size of the carbon fiber strands can be adjusted as well to provide the optimal strength per strand.
- Test Method for Strand Tensile Strength of C-GRID™ Products
(Ref. CTM-001) - Method for Calculating and Reporting C-GRID™ Tensile Properties
(Ref. CTM-002) - Characterization of C-GRID Strand Tensile Strength
- Characterization of C-GRID Cross-Shear Strength
- Comparison of the Tensile Strength of C5500EX1 C-GRIDTM Obtained by Tensile Tests and Concrete Section Tests
- Comparison of the Tensile Strengths of C-GRID™ C5500-AX1 & C5500-ATX Carbon Grids Obtained by Tensile Tests and Concrete Section Tests
- Tensile Strength of C-GRIDTM Products Obtained by Panel Tests
- Probability Distribution of the Strength of Concrete Sections Reinforced with Multiple Grid Elements
- Fatigue Behavior of C-GRID
- Behavior of C-GRID Under Sustained Loads (in work)
- Effects of 100-Year Aging in a High Alkalinity Environment On the Strength of C-GRID™ Carbon/Epoxy Grids
Test Method for Strand Tensile Strength of C-GRID™ Products (Ref. CTM-001)
This test method describes the requirements for sample preparation and tensile testing of the individual strands of C-GRID carbon grid products. TechFab developed the test method for use in quality control, but it may be applied to material characterization and for generating design values.
Method for Calculating and Reporting C-GRID™ Tensile Properties (Ref. CTM-002)
This method describes the procedures used to calculate and report the tensile properties of individual strands as well the tensile properties of C-GRID carbon grid products. The method uses the results of individual strand tensile strength testing and the mechanical and physical properties as reported by the supplier of input fibers in their certifications of conformance. The tensile properties are reported using an “equivalent fiber area” format similar to that described in ACI 440.3R-04 and ACI 440.1R-02.
Characterization of C-GRID Strand Tensile Strength
The objective of the strand tensile strength test is to measure the tensile strength of the individual strands that comprise a C-GRID carbon fiber grid. Washington University, TechFab, and Chomarat have tested samples cut from strands running in both longitudinal and transverse directions. TechFab has conducted over 2000 individual strand tensile tests in order to develop material design values for the grids they manufacture for the AltusGroup. Data is logged into a database rather than published in report format. The average strand tensile strength for a 50k carbon strand (typical in most products used by AltusGroup) is about 1000 lbs.
Characterization of C-GRID Cross-Shear Strength
The objective of the cross-shear test is to measure the bond strength between longitudinal and transverse strands where the cross or intersect. Initially, this property was viewed as important to the strand bond strength to the concrete. The test is similar to the strand tensile strength test except the strand is embedded in a concrete cylinder.
Comparison of the Tensile Strength of C5500EX1 C-GRIDTM Obtained by Tensile Tests and Concrete Section Tests
The objective of the test program is to compare the effective reinforcement strength of C-GRID™ C5500-EX1 used in a concrete section with the statistics for the C-GRID strength obtained by the testing procedures used by TechFab. Testing found that 1) the slab test procedure allows the effective strength of C-GRID at failure to be determined accurately, 2) There is considerably less scatter in the effective strength of C-GRID as determined by slab tests compared to the tensile strength of individual grid elements as determined by tensile tests, and 3) The mean effective strength of C-GRID as determined by slab tests is less than the mean strength determined by strand tests.
Comparison of the Tensile Strengths of C-GRID™ C5500-AX1 & C5500-ATX Carbon Grids Obtained by Tensile Tests and Concrete Section Tests
Similar to 3.5a, but studied C5500-AX1 and C5500-ATX grids.
Tensile Strength of C-GRIDTM Products Obtained by Panel Tests
Similar to 3.5a and 3.5b, but also studied the effect of spacing of longitudinal strands on the effective strength of transverse strands. Testing showed that 1) increasing the space between warp elements has no observable effect on the strength of the weft elements as determined by panel tests, and 2) For fill elements, the effective tensile strengths determined by panel tests are higher than would be expected after accounting for the group effect. This result is believed to be due to the fact that although curvature in fill elements can significantly reduce tensile strength during tensile tests, curvature has little effect on the effective tensile strength obtained from panel tests since the concrete surrounds the element and eliminates induced moment due to the curvature.
Probability Distribution of the Strength of Concrete Sections Reinforced with Multiple Grid Elements
The distribution of the strength of N individual C-GRID elements used as reinforcement for concrete sections can be calculated using Monte Carlo simulation by assuming the strengths of individual elements are uniformly and normally distributed independent random variables. The mean strength decreases with increasing N and cv1 and the coefficient of variation decreases with increasing N. The strength value associated with m-2σ is fairly insensitive to the value of N. Therefore, when m-2σ is given as the characteristic strength value, the value for N = 1 can be used with reasonable confidence for any practical value of N. For large N, there is little difference between the m-2σ value and the m-3σ value since the coefficient of variation is small.
Fatigue Behavior of C-GRID
The objective of the research was to develop an S-N type relationship for the fatigue strength of C-GRID used as flexural reinforcement in reinforced concrete sections. Fatigue information in this format can be used in a multitude of design and code approval situations. A secondary objective of the research was to determine if there is a shift in the S-N curve due to interaction of the C-GRID with the concrete due to friction or other unanticipated interactions. Testing showed that the fatigue performance of C-GRID is excellent.
Behavior of C-GRID Under Sustained Loads (in work)
The objective of the test program is to quantify the behavior under long term sustained loads.
Effects of 100-Year Aging in a High Alkalinity Environment On the Strength of C-GRID™ Carbon/Epoxy Grids
The objective of this study is to examine the effects on the strength of carbon fiber grids subjected to highly alkaline environments for simulated times of 50, 75, and 100 years. It was found that C-GRID carbon fiber grids retain at least 89% of their strength after being subjected to simulated 100-years of exposure to highly alkaline environments based on this study. The high alkali conditions and the 80°C temperature of this study will exceed most conditions encountered in normal use.
