Method and apparatus for measuring properties of concrete

• US 7,289,916 B2
• Filed: 02/28/2005
• Issued: 10/30/2007
• Est. Priority Date: 02/26/2004
• Status: Expired due to Fees

• Current Assignee: Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Original Assignee: Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Inventors: Yu, Xiong, Drnevich, Vincent P.
• Primary Examiner(s): Wachsman; Hal
• Assistant Examiner(s): Desta; Elias
• Application Number:
  US11/067,867
• Publication Number:
  US 20050210995A1
• Time in Patent Office: 974 Days
• Field of Search: 702/43, 702/53, 702/66, 702/138, 702/189, 73/190.8, 73/73, 73788-790, 324/694, 338/35, 340/602, 700/208
• US Class Current: 702/43
• CPC Class Codes: C04B 28/02 containing hydraulic cements other than calcium sulfates
• CPC Class Codes: C04B 40/0032 Controlling the process of mixing, e.g. adding ingredients in a quantity depending on a measured or desired value B28C7/00 takes precedence
• CPC Class Codes: G01N 33/383 Concrete, cement

Abstract

Methods and apparatus using time domain reflectometry to determine electrical properties of concrete for calculating physical and mechanical properties of the concrete that are indicative of concrete quality and durability. The dielectric constant of a concrete is determined to calculate the gravimetric water content of the concrete for use in finding the water-cement ratio of the concrete. Electrical conductivity of curing concrete is determined to calculate compressive strength of the concrete for use in predicting strength development in the concrete.

Claims

1. A method of measuring water content of concrete, comprising the steps of:

placing a plurality of spikes into the concrete;

applying to said plurality of spikes an electrical signal suitable for time domain reflectometry;

analyzing a reflected signal using time domain reflectometry to determine an apparent dielectric constant K_a of the concrete;

calculating gravimetric water content w of the concrete using a predetermined relationship between K_a and a ratio including density of water P_w and total density of the concrete P_t ; and

outputting a result of said calculation.

2. The method of claim 1, wherein said predetermined relationship between K_a and said ratio including density of water P_w and total density of the concrete P_t is

$w=\frac{\sqrt{K_a}}{}$

ρ

w ρ

t - a b - K a ⁢

ρ

w ρ

t ,

where a and b are concrete specific calibration constants.

3. The method of claim 2, wherein said apparent dielectric constant K_a is adjusted to compensate for temperature.

4. The method of claim 3, wherein said adjustment to compensate for temperature comprises adjusting said apparent dielectric constant K_a based upon a linear relationship between K_a at a given temperature and K_a at a reference temperature.

5. The method of claim 1, wherein said electrical signal has a frequency above a relaxation frequency of bound water in the concrete.

6. A method of measuring water-cement ratio of concrete, comprising the steps of:

placing a plurality of spikes into the concrete;

applying to said plurality of spikes an electrical signal suitable for time domain reflectometry;

analyzing a reflected signal using time domain reflectometry to determine an apparent dielectric constant K_a of the concrete;

calculating gravimetric water content w of the concrete using a predetermined relationship between K_a and a ratio including density of water P_w and total density of the concrete P_t;

determining the cement content C;

calculating water-cement ratio of the concrete; and

outputting a result of said water-cement ratio calculation.

7. The method of claim 6, wherein said predetermined relationship between K_a and said ratio including density of water P_w and total density of the concrete P_t is

$w=\frac{\sqrt{K_a}}{}$

ρ

w ρ

t - a b - K a ⁢

ρ

w ρ

t ,

where a, and b are concrete specific calibration constants.

8. The method of claim 7, wherein said apparent dielectric constant K_a is adjusted to compensate for temperature.

9. The method of claim 8, wherein said adjustment to compensate for temperature comprises adjusting said apparent dielectric constant K_a based upon a linear relationship between K_a at a given temperature and K_a at a reference temperature.

10. The method of claim 6, wherein said electrical signal has a frequency above a relaxation frequency of bound water in the concrete.

11. A method of predicting compressive strength development of concrete, comprising steps of:

placing a plurality of spikes into the concrete;

applying to said plurality of spikes an electrical signal suitable for time domain reflectometry;

analyzing a reflected signal using time domain reflectometry to determine electrical conductivity EC_b of the concrete;

predicting compressive strength f_c of the concrete based upon EC_b decreasing log-linearly in time; and

outputting a result of said prediction.

12. A method of predicting compressive strength development of concrete, comprising steps of:

placing a plurality of spikes into the concrete;

applying to said plurality of spikes an electrical signal suitable for time domain reflectometry;

analyzing a reflected signal using time domain reflectometry to determine electrical conductivity EC_b of the concrete;

predicting compressive strength f_c based upon a predetermined relationship of

$f_c=\mathrm{\alpha <br><br>}<br><br>\left[\frac{\mathrm{\pi <br><br>}}{2}-{\tan }^{-1}<br><br>\left\{\mathrm{\beta <br><br>}<br><br>\left[{\mathrm{EC}}_b<br><br>\left(t_1\right)+\left(\frac{\mathrm{\Delta <br><br>}<br><br><br><br>{\mathrm{EC}}_b}{\log <br><br><br><br>\mathrm{cycle}}\right)<br><br>\log <br><br>\left(t\right)-{\mathrm{EC}}_0\right]\right\}\right]<br><br>P_a,$

where α

is an empirical constant, β

is an empirical constant, EC_b(t₁) is said electrical conductivity EC_b measured at one day, Δ

EC_b/(log cycle) is change in said electrical conductivity over one log cycle, EC₀ is obtained from calibration tests, and P_a is atmospheric pressure; and

outputting a result of said prediction.

13. The method of claim 12, wherein said electrical conductivity EC_b is adjusted to compensate for temperature.

14. The method of claim 13, wherein said adjustment to compensate for temperature comprises adjusting said electrical conductivity EC_b based upon a linear relationship between EC_b at a given temperature and EC_b at a reference temperature.

15. An apparatus for measuring water content of concrete, comprising:

a plurality of spikes adapted to be placed into the concrete;

means for applying to said plurality of spikes an electrical signal suitable for time domain reflectometry;

means for analyzing a reflected signal using time domain reflectometry to determine an apparent dielectric constant K_a of the concrete;

means for calculating gravimetric water content w of the concrete using a predetermined relationship between K_a and a ratio including density of water P_w and total density of the concrete P_{t; and}

means for outputting a result of said calculation.