Methods and systems for manufacturing optimized concrete Number:7,386,368 from the United States Patent and Trademark Office (PTO) owispatent Design optimization methods can be used to design concrete mixtures having optimized properties, including desired strength and slump at minimal cost. The design optimization methods use a computer-implemented process that is able to design and virtually "test" millions of hypothetical concrete compositions using mathematical algorithms that interrelate a number of variables that affect strength, slump, cost and other desired features. The design optimization procedure utilizes a constant K (or K factor) within Feret's strength equation that varies (e.g., logarithmically) with concrete strength for any given set of raw material inputs and processing equipment. That means that the binding efficiency or effectiveness of hydraulic cement increases with increasing concentration so long as the concrete remains optimized. The knowledge of how the K factor varies with binding efficiency and strength is a powerful tool that can be applied in multiple circumstances. A concrete manufacturing process may include accurately measuring the raw materials to minimize variation between predicted and actual strength, as well as carefully controlling water content throughout the manufacturing and delivery process.<H manufacturing, optimized, Methods, and, sys, 7386368.html, Patent, pto, 7386368

Title: Methods and systems for manufacturing optimized concrete

Abstract: Design optimization methods can be used to design concrete mixtures having optimized properties, including desired strength and slump at minimal cost. The design optimization methods use a computer-implemented process that is able to design and virtually "test" millions of hypothetical concrete compositions using mathematical algorithms that interrelate a number of variables that affect strength, slump, cost and other desired features. The design optimization procedure utilizes a constant K (or K factor) within Feret's strength equation that varies (e.g., logarithmically) with concrete strength for any given set of raw material inputs and processing equipment. That means that the binding efficiency or effectiveness of hydraulic cement increases with increasing concentration so long as the concrete remains optimized. The knowledge of how the K factor varies with binding efficiency and strength is a powerful tool that can be applied in multiple circumstances. A concrete manufacturing process may include accurately measuring the raw materials to minimize variation between predicted and actual strength, as well as carefully controlling water content throughout the manufacturing and delivery process.

Patent Number: 7,386,368 Issued on 06/10/2008 to Andersen, et al.

Inventors: Andersen; Per Just (Santa Barbara, CA), Hodson; Simon K. (Santa Barbara, CA)
Assignee: Icrete, LLC (Beverly Hills, CA)

Appl. No.: 11/858,610

Filed: September 20, 2007

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
11471293	Jun., 2006
60691916	Jun., 2005

Current U.S. Class: 700/265

Field of Search: 700/117,173,265

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Primary Examiner: DeCady; Albert
Assistant Examiner: Rapp; Chad
Attorney, Agent or Firm: Workman Nydegger

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 11/471,293, filed Jun. 19, 2006, which claims the benefit under 35 U.S.C. .sctn. 119(e) of U.S. Provisional Application Ser. No. 60/691,916, filed Jun. 17, 2005. This application also claims the benefit of earlier filed and co-pending International Application No. PCT/US06/23863, filed Jun. 19, 2006, which claims the benefit of U.S. Provisional Application Ser. No. 60/691,916, filed Jun. 17, 2005. The disclosures of the foregoing applications are incorporated herein in their entirety.

Claims

What is claimed is:

1. A method of manufacturing a concrete composition comprising: obtaining a concrete mix design prepared at least in part by: inputting into a computing system data relating to particle size and particle packing density for a plurality of solid components; inputting into the computing system a target strength; inputting into the computing system a selected design K factor for use in determining a predicted strength for each of a plurality of concrete mix designs generated by the computing system, the design K factor being selected based on the target strength from among a plurality of different K factors that vary with concrete strength for the given set of raw materials; the computing system designing a plurality of concrete mix designs having varying quantities of raw materials; the computing system identifying an amount of water for each of the concrete mix designs; the computing system determining, based on the selected design K factor and the identified amount of water, a predicted strength for each of the concrete mix designs; and the computing system comparing the predicted strength for each concrete mix design with the target strength to identify a concrete mix design that is better optimized with respect to strength compared to other of the plurality of concrete mix designs; and manufacturing a concrete composition according to the concrete mix design or a corrected variation thereof.

2. A method as defined in claim 1, the concrete, composition having a substantially optimized ratio of raw materials.

3. A method as defined in claim 1, the concrete mix design being further prepared by: inputting into the computing system data relating to raw materials cost; and the computing system identifying the better optimized concrete mix design at least on part on the basis of having a lower cost compared to other of the plurality of concrete mix designs.

4. A method as defined in claim 1, wherein the selected design K factor accounts for an effect on concrete strength of including an amine strengthener, the method further comprising adding an amine strengthener to the concrete composition.

5. A method as defined in claim 1, wherein the selected design K factor accounts for an effect on concrete strength of including at least one of fly ash or silica fume, the method further comprising adding at least one of fly ash or silica fume to the concrete composition.

6. A method as defined in claim 1, wherein the selected design K factor accounts for an effect on concrete strength of using a specific mixing apparatus, the method further comprising mixing the concrete composition using the specific mixing apparatus.

7. A method as defined in claim 1, further comprising: preparing a concrete test sample for a given set of raw materials based on the concrete mix design; determining a strength for the concrete test sample; and altering the concrete mix design to obtain a corrected variation of the concrete mix design for the given set of raw materials that yields a concrete composition having a strength that more closely correlates with the target strength compared to the selected concrete mix design.

8. A method as defined in claim 1, further comprising: preparing a concrete test sample for a given set of raw materials based on the concrete mix design; determining a slump for the concrete test sample; and altering the concrete mix design to obtain a corrected variation of the concrete mix design for the given set of raw materials that yields a concrete composition having a slump that more closely correlates with the target slump compared to the selected concrete mix design.

9. A method as defined in claim 1, further comprising: upgrading and/or recalibrating equipment used by the manufacturing plant in manufacturing concrete so that concrete manufactured by the manufacturing plant using the upgraded and/or recalibrated equipment has an actual strength that more closely correlates to design strength compared to previous equipment prior to upgrading and/or recalibrating.

10. A method as defined in claim 1, further comprising: the computing system identifying a modified mix design that yields a concrete composition having a modified slump but substantially similar strength by altering a ratio of cement paste to aggregate relative to the selected concrete mix design or corrected variation thereof; and manufacturing a modified concrete composition according to the modified mix design or corrected variation thereof.

11. A method of manufacturing a concrete composition comprising: identifying a pre-existing concrete mix design having an initial ratio of components, a design strength, and an apparent design K factor based on actual strength of concrete manufactured using the pre-existing concrete mix design; obtaining a revised concrete mix design prepared at least in part by a computer system designing a revised concrete mix design having a revised ratio of components using a revised design K factor that is selected based on the design strength and that more closely corresponds to an optimal K factor corresponding to the design strength compared to the apparent K factor of the pre-existing concrete mix design; and manufacturing a concrete composition according to the revised concrete mix design or a corrected variation thereof.

12. A method as defined in claim 11, wherein the concrete composition has an actual strength that more closely corresponds to the design strength compared to concrete compositions made using the pre-existing concrete mix design.

13. A method as defined in claim 11, the concrete composition having a better optimized ratio of raw materials compared to concrete compositions made using the pre-existing concrete mix design so as to have the specific minimum strength at a given slump and at lower cost compared to concrete compositions made using the pre-existing concrete mix design.

14. In an existing concrete manufacturing plant that manufactures a plurality of different concrete compositions having different design strengths, a method of manufacturing concrete compositions that have actual strengths that more closely correlate with their respective design strengths, the method comprising: identifying a plurality of pre-existing concrete mix designs of the concrete manufacturing plant in need of better optimization, wherein at least two of the mix designs have differing design strengths; obtaining a pluraility of new or revised concrete mix designs having new or revised ratios of components compared to the pre-existing concrete mix designs, the new or revised concrete mix designs being prepared at least in part by: selecting a plurality of different design K factors for use in designing better optimized concrete mix designs, wherein the different K factors correlate with and vary based on differing selected design strengths; and designing, using the plurality of different design K factors, the plurality of new or revised concrete mix designs; and manufacturing, based on the new or revised concrete mix designs or corrected variations thereof, revised concrete compositions having actual strengths that more closely correlate with their respective design strengths compared to pre-existing concrete compositions previously manufactured using the pre-existing mix designs, wherein the revised concrete compositions each have an actual strength at a given slump that more closely correlates to its respective design strength compared to the pre-existing concrete compositions.

15. A method as defined in claim 14, further comprising making slump adjustments to one or more of the revised concrete compositions by adding or altering an amount of an admixture within the one or more concrete compositions.

16. A method as defined in claim 14, further comprising upgrading and/or adjusting production equipment utilized by the manufacturing plant so that each component is weighed or otherwise measured with an accuracy of about .+-.2.0%.

17. A method as defined in claim 14, further comprising monitoring moisture content of solid components and altering measured amounts of solid components and added batch water used to manufacture a concrete composition based on detected changes in the moisture content of the solid components.

18. A method as defined in claim 14, further comprising delivering a concrete composition using a concrete mixing truck that includes a vessel containing an admixture that alters slump and metering a selected amount of the admixture into a mixing drum carrying the concrete composition in order to alter slump in a desired manner.

19. In a concrete manufacturing plant having a given set of raw material components, a method of manufacturing concrete compositions having actual strengths that more closely reflect their predicted or design strengths compared to less optimized concrete compositions made from the given set of raw material components, the method comprising: obtaining a plurality of optimized concrete mix designs having different design strengths that were designed using different design K factors, wherein each different design K factor was selected at least in part based on its respective design strength; and manufacturing a plurality of optimized concrete compositions based on the optimized concrete mix designs or corrected variations thereof, each optimized concrete composition having an optimized ratio of components so as to have an actual strength that more closely reflects its predicted or design strength compared to a less optimized concrete composition made from the given set of raw material components.

20. A method as defined in claim 19, further comprising making slump adjustments to one or more of the optimized concrete compositions by adding or altering an amount of an admixture within the one or more concrete compositions.

21. A method as defined in claim 19, further comprising weighing or otherwise measuring the components of each concrete composition with an accuracy of about .+-.2.0%.

22. A method as defined in claim 19, further comprising monitoring moisture content of solid components and altering a measured amount of solid components and added batch water used to manufacture a concrete composition based on detected changes in the moisture content of the solid components.

23. A method as defined in claim 19, further comprising mixing one or more of the optimized concrete compositions using a concrete mixing truck that includes a vessel containing an admixture for adjusting slump and metering a selected amount of the admixture into a mixing drum carrying the concrete composition in order to alter slump in a desired manner.

24. A method of manufacturing a concrete composition that is better optimized compared to an existing concrete composition having a given design strength and ratio of components and that is overdesigned without having to (i) prepare a concrete test sample, (ii) allow it to harden, (iii) test its actual strength, and (iv) compare the actual strength of the test sample with the given design strength, the method comprising: obtaining a revised concrete mix design for use in manufacturing a concrete composition that is better optimized compared to the existing concrete composition, the revised concrete mix design being prepared at least in part by: determining an apparent design K factor for the existing concrete composition based on the given design strength of the concrete composition and the given ratio of components within the concrete composition; comparing the apparent design K factor with a more optimal K factor that corresponds to the given design strength and which is selected from among a plurality of different K factors that vary with varying concrete strength; redesigning the existing concrete composition to yield the revised concrete mix design by means of an optimization procedure that utilizes a revised design K factor that more closely correlates with an optimal K factor for the given design strength, wherein the revised concrete mix design from the optimization procedure yields a revised concrete composition having an actual strength that more closely correlates with the design strength compared to the existing concrete composition; and manufacturing a concrete composition based on the revised concrete mix design or a corrected variation thereof.

25. A method as defined in claim 24, further comprising modifying the revised concrete mix design to yield a modified concrete mix design and manufacturing a modified concrete composition according to the modified concrete mix design.

Description

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The invention is in the field of concrete compositions, more particularly in the design-optimization of concrete compositions based on factors such as performance and cost. The invention more particularly relates to the design and manufacture of concrete using improved methods that more efficiently utilize all the components from a performance and cost standpoint and minimize strength variability, as well as unique methods for redesigning an existing concrete mix design and upgrading the batching, mixing and/or delivery system of an existing concrete manufacturing plant.

2. The Relevant Technology

Concrete is a ubiquitous building material. Finished concrete results from the hardening of an initial cementitious mixture that typically comprises hydraulic cement, aggregate, water, and optional admixtures. The terms "concrete", "concrete composition" and "concrete mixture" shall mean either the finished, hardened product or the initial unhardened cementitious mixture depending on the context. It may also refer to the "mix design", which is the formula or recipe used to manufacture a concrete composition. In a typical process for manufacturing transit mixed concrete, the concrete components are added to and mixed in the drum of a standard concrete delivery truck, typically while the truck is in transit to the delivery site. Hydraulic cement reacts with water to form a binder that hardens over time to hold the other components together.

Concrete can be designed to have varying strength, slump, and other materials characteristics, which gives it broad application for a wide variety of different uses. The raw materials used to manufacture hydraulic cement and concrete are relatively inexpensive and can be found virtually everywhere although the characteristics of the materials can vary significantly. This allows concrete to be manufactured throughout the world close to where it is needed. The same attributes that make concrete ubiquitous (i.e., low cost, ease of use, and wide availability of raw materials) have also kept it from being fully controlled and its full potential developed and exploited.

Concrete manufacturing plants typically offer and sell a number of different standard concrete compositions that vary in terms of their slump and strength. Each concrete composition is typically manufactured by following a standard mix design, or recipe, to yield a composition that has the desired slump and that will harden into concrete having the desired strength. Unfortunately, there is often high variability between the predicted (or design) strength of a given mix design and the actual strength between different batches, even in the absence of substantial variability in the quality or characteristics of the raw material inputs. Part of this problem results from a fundamental disconnect between the requirements, controls and limitations of "field" operations in the concrete batch plant and the expertise from research under laboratory conditions. Whereas experts may be able to design a concrete mixture having a predicted strength that closely reflects actual strength when mixed, cured and tested, experts do not typically prepare concrete compositions at concrete plants for delivery to customers. Concrete personnel who batch, mix and deliver concrete to job sites inherently lack the ability to control the typically large variation in raw material inputs that is available when conducting laboratory research. The superior knowledge of concrete by laboratory experts is therefore not readily applicable or transferable to the concrete industry in general.

In general, concrete mixtures are designed based on such factors as (1) type and quality of hydraulic cement, (2) type and quality of aggregates, (3) quality of water, and (4) climate (e.g., temperature, humidity, wind, and amount of sun, all of which can cause variability in slump, workability, and strength of concrete). To guarantee a specific minimum strength and slump as required by the customer (and avoid liability in the case of failure), concrete manufacturers typically follow a process referred to as "overdesign" of the concrete they sell. For example, if the 28 day field strength of a particular concrete mix design is known to vary between 2500 psi and 4000 psi when manufactured and delivered, a manufacturer must typically provide the customer with a concrete composition based on a mix design that achieves a strength of 4000 psi under controlled laboratory conditions to guarantee the customer a minimum strength of 2500 psi through the commercial process. Failure to deliver concrete having the minimum required strength can lead to structural problems, even failure, which, in turn, can leave a concrete plant legally responsible for such problems or failure. Thus, overdesigning is self insurance against delivering concrete that is too weak, with a cost to the manufacturer equal to the increased cost of overdesigned concrete. This cost must be absorbed by the owner, does not benefit the customer, and, in a competitive supply market, cannot easily be passed on to the customer.

Overdesigning typically involves adding excess hydraulic cement in an attempt to ensure a minimum acceptable strength of the final concrete product at the desired slump. Because hydraulic cement is typically the most expensive component of concrete (besides special admixtures used in relatively low amounts), the practice of overdesigning concrete can significantly increase cost. However, adding more cement does not guarantee better concrete, as the cement paste binder is often a lower compressive strength structural component compared to aggregates and the component subject to the greatest dynamic variability. Overcementing can result in short term microshrinkage and long term creep. Notwithstanding the cost and potentially deleterious effects, it is current practice for concrete manufacturers to simply overdesign by adding excess cement to each concrete composition it sells than to try and redesign each standard mix design. That is because there is currently no reliable or systematic way to optimize a manufacturer's pre-existing mix designs other than through time-consuming and expensive trial and error testing to make more efficient use of the hydraulic cement binder and/or account for variations in raw material inputs.

The cause of observed strength variability is not always well understood, nor can it be reliably controlled using existing equipment and following standard protocols at typical ready-mix manufacturing plants. Understanding the interrelationship and dynamic effects of the different components within concrete is typically outside the capability of concrete manufacturing plant employees and concrete truck drivers using existing equipment and procedures. Moreover, what experts in the field of concrete might know, or believe they know, about concrete manufacture, cannot readily be transferred into the minds and habits of those who actually work in the field (i.e., those who place concrete mixtures into concrete delivery trucks, those who deliver the concrete to a job site, and those who place and finish the concrete at job sites) because of the tremendous difference in controls and scope of materials variation. The disconnect between what occurs in a laboratory and what actually happens during concrete manufacture can produce flawed mix designs that, while apparently optimized when observed in the laboratory, may not be optimized in reality when the mix design is scaled up to mass produce concrete over time.

Besides variability resulting from poor initial mix designs, another reason why concrete plants deliberately overdesign concrete is the inability to maintain consistency of manufacture. There are four major systemic causes or practices that have historically lead to substantial concrete strength variability: (1) the use of materials that vary in quality and/or characteristics; (2) the use of inconsistent batching procedures; (3) overcementing; and (4) adding insufficient batch water initially and later making slump adjustments at the job site, typically by the concrete truck driver adding an uncontrolled amount of water to the mixing drum. The total variation in materials and practices can be measured by standard deviation statistics.

The first cause of variability between theoretical and actual concrete strengths for a given mix design is variability in the supply of raw materials. For example, the particle size, size distribution, morphology, and particle packing density of the hydraulic cement and aggregates (e.g., course, medium, and fine) may vary from batch to batch. Even slight differences can greatly affect how much water must be added to yield a composition having the required slump. Because concrete strength is highly dependent on the water-to-cement ratio, varying the water content to account for variations in the solid particle characteristics to maintain the required slump causes substantial variability in concrete strength. Unless a manufacturer can eliminate variations in raw material quality, overdesigning is generally the only available way to ensure that a concrete composition having the required slump also meets the minimum strength requirements.

Even if a concrete manufacturer accounts for variations in raw materials quality, overdesigning is still necessary using standard mix design tables. Standardized tables are based on actual mix designs using one type and morphology of aggregates that have been prepared and tested. They provide slump and strength values based on a wide variety of variables, such as concentration of cement, aggregates, water, and any admixtures, as well as the size of the aggregates. The use of standardized tables is fast and simple but can only approximate actual slump and strength even when variations in raw materials are measured. That is because the number of standardized mix designs is finite though the variability in the type, quality and concentration (i.e., ratio) of raw materials is virtually infinite. Because standardized tables can only approximate real world raw material inputs, there can be significant variability between predicted and actual strength when using mix designs from standardized tables. Because of this variability, the only two options are (1) time consuming and expensive trial and error testing to find an optimal mix design for every new batch of raw materials or (2) overdesigning. Manufacturers typically opt for overdesigning, especially in light of factors other than mix design that cause variations between design and actual strength.

The second cause of strength variability is the inability to accurately deliver the components required to properly prepare each batch of concrete. Whereas modern scales can theoretically provide very accurate readings, sometimes to within 0.05% of the true or actual weight, typical hoppers and other dispensing equipment used to dispense the components into the mixing vessel (e.g., the drum of a concrete mixer truck) are often unable to consistently open and shut at the precise time in order to ensure that the desired quantity of a given component is actually dispensed into the mixing vessel. To many concrete manufacturers, the perceived cost of upgrading or properly calibrating their metering and dispensing equipment is higher than simply overdesigning the concrete, particularly since most manufacturers have no idea how much the practice of overdesigning concrete actually costs and because it is thought to be a variable cost rather than a capital cost.

Overdesigning often leads to the third cause of strength variability, which is overcementing. Overcementing involves increasing the amount of hydraulic cement in an attempt to achieve or guarantee a minimum strength by overcoming the effect on strength by randomly adding water after batching to adjust slump. This, however, can lead to increases in strength variability, as hardened cement paste is typically weaker as a structural element compared to the aggregate components. While adding more cement may increase the binding strength provided by the cement paste that holds the aggregates together, more cement can also weaken concrete by displacing stronger aggregate materials with the weaker cement paste as a structural component of the hardened concrete. Strength variability occurs as a result of the foregoing effects working in opposite directions, but in differing amounts between different batches of concrete (e.g., due to differences in the water-to-cement ratio, quality and characteristics of the hydraulic cement, aggregates and water, and how the concrete is handled when delivered to a job site).

Overcementing can also cause microshrinkage, particularly on or near the surface due to water evaporation, which reduces the strength and durability of the concrete surface. Microshrinkage caused by overcementing and poor component distribution can cause cracks and crazing within 1-2 years of manufacture. Overcementing can also cause creep, which is the dynamic (and usually undesirable) growth of concrete masses due to continued long term hydration and growth of hydration products of the cement grains,

The fourth cause of concrete strength variability is the practice by concrete truck drivers of adding water to concrete after batching in an attempt to improve or modify the concrete to make it easier to pour, pump, work, and/or finish. In many cases, concrete is uniformly designed and manufactured to have a standard slump (e.g., 3 inch) when the concrete truck leaves the lot, with the expectation that the final slump requested by the customer will be achieved on site through the addition of water. This procedure is imprecise because concrete drivers rarely, if ever, use a standard slump cone to actually measure the slump but simply go on "look and feel". Since adding water significantly decreases final concrete strength, the concrete plant must build in a corresponding amount of increased initial strength to offset the possible or expected decrease in strength resulting from subsequent water addition. Because strength can be decreased by varying amounts depending on the actual amount of water added by the driver, the manufacturer must assume a worst-case scenario of maximum strength loss when designing the concrete in order to ensure that the concrete meets or exceeds the required strength.

Given the foregoing variables, which can differ in degree and scope from day to day, a concrete manufacturer may believe it to be more practical to overdesign its concrete compositions rather than account and control for the variables that can affect concrete strength, slump and other properties. Overdesigning, however, is not only wasteful as an inefficient use of raw materials, sometimes providing concrete that is substantially stronger than what is required can also be dangerous. For example, because stronger concrete is often more brittle than weaker concrete, it can fail before the weaker concrete when subjected to the forces of an earthquake.

In an effort to more efficiently design concrete compositions and take into account variations in the particle size, particle size distribution, morphology, and packing densities of the various solid components between different batches of cement and aggregates, the inventors previously developed a design optimization process that greatly improved upon traditional methods for designing concrete mixtures. This process is described in U.S. Pat. No. 5,527,387 to Andersen et al., entitled "Design Optimized Compositions and Computer Implemented Processes for Microstructurally Engineering Cementitious Mixtures" (hereinafter "Andersen patent"). For brevity, the design optimization process disclosed in the Andersen patent will be referred to as the "DOC program" (the term "DOC" being an acronym for "design optimized concrete").

The DOC program mathematically relates the properties of strength, slump and other aspects, such as cost, cohesiveness and durability, based on the concentrations and qualities of the various raw material inputs. The DOC program is able to design and virtually "test" millions of different hypothetical mix designs in seconds using a computer. This greatly reduces the amount of time required to carry out trial-and-error testing that would otherwise be necessary to identify a concrete mixture that is optimized for strength, slump, cost and/or other desired features. The goal of the DOC program is to identify an optimal mix design, from among a large number of hypothetical mix designs, based on such desired features as slump, strength, and cost. The DOC program fills in gaps inherent in standardized tables, which include a relatively small number of mix designs given the variability of raw material inputs. The DOC program can design and virtually "test" millions of different mix designs, including those falling between the gaps of standardized tables, in much less time than it takes to design and test one mix design using conventional trial-and-error methods.

First, the raw materials are carefully tested to determine characteristics that affect the slump, strength, cost, and/or other desired features of cementitious compositions made therefrom. These include, for example, the particle size and packing density of the various aggregate components (e.g., large, medium and small aggregates) and hydraulic cement particles, and the effect of one or more optional admixtures (e.g., fly ash, water reducers, fillers, etc.). Once the raw materials have been characterized with the required degree of accuracy, their characteristics are input into a computer used to carry out the optimization process of the DOC program.

Thereafter, the DOC program designs a large number of hypothetical concrete mixtures, each having a theoretical slump and strength, by varying the concentrations of cement, aggregate, water, and optional admixtures. The predicted slump and strength of each hypothetical concrete mixture is determined by inputting the variables (e.g., the concentration and characteristics of the raw materials) into a system of interrelated mathematical equations. One of the equations utilized in the DOC program is a variation of Feret's strength equation, which states that the compressive strength of the final hardened concrete composition is proportional to the square of the volumetric ratio of hydraulic cement to cement paste, which consists of cement, water and air:

.sigma. ##EQU00001##

The constant "K" within this equation provides proper strength units and magnitude. The strength equation can be modified as follows to predict the strength of concrete that additionally includes other binders, such as class F fly ash, as part of the cement paste:

.sigma..times..times. ##EQU00002##

The DOC program can be carried out in an iterative manner in which each iteration yields a hypothetical concrete mixture having a predicted slump and strength that is closer to the desired slump and strength than each previous iteration. In addition to slump and strength, the DOC program can optimize concrete for other desired features, such as cost, workability, or cohesion. Thus, in the case where a number of different concrete mixtures may have the desired slump and strength, the DOC program can identify which of the mixtures is "optimal" according to one or more other criteria (e.g., cost, workability and/or cohesion).

Notwithstanding the foregoing, the DOC program, when initially invented, was based on the assumption, well-accepted in the art, that the constant K (or "K factor") within Feret's strength equation is a true constant and does not vary as long as the same type of mixing apparatus and source of raw materials are used each time. It has been well-accepted in the art that if such variables are kept constant, the K factor remains constant regardless of variations in hydraulic cement concentration and concrete strength. As a result of this well-accepted assumption, the DOC program required significant post-design corrections, even significant testing and redesign of concrete compositions made using one or more of the "optimal" mix designs generated by the program. Thus, the inability of the DOC program to account for dynamic variability of the K factor limited the practical application of an otherwise powerful design optimization tool.

SUMMARY OF THE INVENTION

It has now been discovered that the constant K (or "K factor") within Feret's strength equation is not a constant but varies depending on the efficiency with which hydraulic cement is able to bind or glue the aggregate particles together. That is true even if the mixing apparatus, aggregate strength, and other factors that affect strength are kept constant. The K factor, which dynamically varies with the binding efficiency of the hydraulic cement binder, can be empirically determined based on concrete strength. Knowing the dynamic variability of the K factor allows for more accurate predictions of concrete strength when performing a design optimizing procedure compared to an optimization procedure that assumes the K factor remains constant so long as the mixing apparatus and raw materials also remain constant. The inventive optimization procedure (hereinafter "improved DOC process") efficiently identifies one or more optimized mix designs with less trial and error testing since using the correct K factor in the first instance naturally reduces the need to correct for errors that would otherwise arise by using an incorrect K factor to predict concrete strength.

Although the binding efficiency of hydraulic cement, and therefore the K factor, cannot be readily measured directly, the K factor for a given concrete composition can be determined indirectly. By rearranging Feret's equation, one can solve for K by knowing the compressive strength, hydraulic cement volume and cement paste volume. By testing a range of standard concrete compositions sold by various manufacturers and then solving for K, the inventors surprisingly found that the K factor varied with actual concrete strength, more particularly, that the K factor of properly prepared concrete increased with increasing compressive strength and follows a logarithmic curve. The logarithmic curve has a theoretical limit corresponding to a concrete composition having perfect component distribution and binding efficiency of the paste system, which only occurs at very high strength (e.g., containing the most optimal paste to aggregate ratio and a water-to-cement ratio of about 0.17 and having perfect distribution of paste and aggregates throughout the concrete composition). At lower strengths representative of typical manufacturing needs and specifications, the K factor lies below the theoretical limit. This indicates that hydraulic cement is not able to realize its highest theoretical binding efficiency at lower strengths, but only approaches it at higher strengths.

Knowing how the K factor, and therefore the binding efficiency of hydraulic cement, varies with strength greatly increases the accuracy by which an optimization procedure that utilizes an appropriate strength equation can predict concrete strength for a large number of hypothetical mix designs. On the other hand, the K factor is independent of changes in slump caused by changing water concentration and/or variations in the size and/or morphology of aggregates. Using the foregoing principles regarding K factor, the improved DOC process can more accurately identify one or more optimized mix designs from among many hypothetical mix designs. The improved DOC process efficiently yields optimized concrete compositions that guarantee a specific minimum slump and strength at the lowest cost and with minimum variability due to poor design. The improved DOC process is more efficient than the original DOC program because knowing in advance how the K factor varies with strength minimizes the amount of post design corrections (e.g., through trial-and-error testing) that might otherwise be required.

One goal of the improved DOC process is to yield optimized mix designs that substantially reduce concrete overdesign compared to conventional mix designs used by concrete manufacturers. In one aspect of the invention, the improved DOC process can be used to create one or more optimized mix designs that guarantee concrete having a specific minimum slump and strength while also reducing the wasted cost caused by overdesign. Another aspect involves dynamically optimizing concrete mix designs based on feedback regarding variations in different batches of raw materials. In yet another aspect, the improved DOC process can be used to re-design one or more existing mix designs of a concrete manufacturer. Identifying variations between the actual (or apparent) design K factor of an existing mix design and the optimal or theoretical K factor corresponding to the design strength can be used to determine the existence and degree of concrete overdesign. Improving the mix design to better utilize the hydraulic cement and optimize binding efficiency of the cement paste can by itself reduce strength variability and the need to overdesign to account for such variability.

In addition to providing optimized mix designs, improving the correlation between predicted strength and actual strength can be further enhanced by upgrading and/or recalibrating plant equipment to better ensure that a manufacturer is able to accurately measure and dispense the raw materials used to manufacture concrete. Such upgrades may not be economically practical in the case where a plant uses poor mix designs. Perfectly calibrated equipment cannot manufacture concrete that is any better than a poor mix design will allow. The use of optimized mix designs therefore allows the manufacturer to obtain the full benefit of any capital equipment upgrades. Because improving plant equipment alone may not yield much benefit, and because optimized mix designs cannot by themselves overcome variability imparted by faulty equipment, improving plant equipment and optimizing mix designs allows both improvements to realize their full potential, thus indicating a synergistic relationship.

In one embodiment, the present invention provides improved methods for designing and manufacturing optimized concrete mix designs utilizing a strength equation that employs a unique K factor value, which varies and is selected depending on the inherent efficiency of component use of the resulting concrete composition (e.g., as empirically predicted by the desired minimum, or "design strength"), all other things being equal. Knowing how the K factor varies with concrete strength greatly improves the ability to accurately and efficiently design an optimized concrete composition because it reduces or minimizes variability between design and actual strength. Minimizing variability between the design strength and actual strength reduces the amount of trial-and-error testing that might otherwise be required to identify a concrete mix design that is truly optimized for slump and strength at minimum cost.

As compared to conventional methods for designing concrete using standardized tables, the improved DOC process more precisely considers the actual characteristics of raw materials utilized by a concrete manufacturer. Standardized tables only roughly approximate actual slump and strength because the characteristics of raw materials presumed in the tables rarely, if ever, reflect the true characteristics of raw materials actually used by a concrete manufacturer. Each concrete manufacturing plant utilizes raw materials that are unique to that plant, and it is unreasonable to expect standardized tables to accurately account for materials variability among different plants. The improved DOC process is able to virtually "test" mix designs that more accurately reflect the raw materials actually utilized by the plant at a given time. By accounting for variations in the quality of raw materials, the improved DOC process is able to substantially reduce the degree of overdesigning of concrete compositions that might otherwise occur using standardized mix design tables and methods.

Another aspect of the invention involves the redesigning of one or more pre-existing mix designs used by a manufacturing plant to manufacture its commercial concrete compositions. In one embodiment, the method first involves, as a threshold matter, determining whether and by how much an existing concrete composition is overdesigned. Every concrete composition has a design strength, which is typically determined by the minimum strength that must be guaranteed for that composition, and an actual strength that can be measured by properly preparing concrete under absolute controls based on the mix design and testing its strength. Because of the tendency of manufacturers to overdesign to account for expected strength variabilities from batch to batch, there can be a substantial difference between the apparent design K factor based on the guaranteed minimum strength of a concrete mix design and the actual or "true" K factor based on the actual strength of the concrete when properly manufactured according to the mix design.

The extent to which an existing concrete mix design is overdesigned can be ascertained by: (1) properly preparing a concrete test sample according to the existing mix design; (2) allowing the concrete composition to harden; (3) measuring the actual strength of the hardened concrete composition; and (4) comparing the actual strength of the concrete composition with the design strength of the existing mix design. The amount by which the actual strength deviates from the design strength corresponds to the degree by which the existing mix design is overdesigned. The foregoing process requires an amount of time that is necessary for the concrete composition to cure sufficiently in order to accurately measure actual strength.

The degree of overdesign can alternatively be determined in a more expedited fashion by: (1) determining an apparent design K factor of the existing concrete mix design based on the design strength and ratio of components within a concrete composition made according to the existing mix design; (2) identifying an optimal theoretical K factor corresponding to the design strength; and (3) comparing the apparent design K factor of the existing concrete mix design with the optimal K factor that corresponds to the design strength. The amount by which the apparent design K factor deviates from the optimal K factor corresponds to the degree by which the existing mix design is overdesigned. Knowledge of how the optimal K factor varies with concrete strength can therefore be used as a diagnostic tool to determine whether and by how much a pre-existing mix design is overdesigned without waiting for a concrete test sample to harden.

After determining that a pre-existing mix design is overdesigned, an optimized concrete mix design can be designed using the improved DOC process. After selecting a design strength representing the guaranteed specified minimum strength, a revised or corrected K factor corresponding to the design (or desired) strength is selected and used in the improved DOC process. An iterative optimization process utilizing one or more algorithms, including Feret's equation employing the revised design K factor, designs and virtually tests a number of hypothetical concrete compositions in order to identify one or more mix designs optimized for a specified minimum strength and slump having the lowest cost or other desired factors. An optimized mix design reduces variability between design strength and actual strength compared to the pre-existing concrete mix design, thereby reducing overdesign and cost of the resulting concrete composition. By correctly readjusting the relative concentrations of the various components, the improved DOC process improves the binding efficiency of the hydraulic cement binder and reduces how much cement is required to ensure the specified strength requirement. Overcementing can be greatly reduced or eliminated.

In summary, by utilizing correct K factors selected based on design strength, the improved DOC program can accurately and efficiently redesign each standard pre-existing concrete mix design utilized by the manufacturing plant in order to improve the binding efficiency of the cement binder. This reduces or eliminates overdesigning and reduces cost. An existing concrete manufacturing plant can be upgraded simply by providing optimized concrete mix designs even without upgrading and/or recalibrating the manufacturing plant equipment.

Variations between actual strength and design strength can be further minimized by properly controlling the preparation and handling of the concrete compositions. Some retooling may be necessary to ensure that the batching and weighing equipment meets standard ASTM-94 requirements. Thus, according to another aspect of the invention, affirmative steps can be taken to better control the measuring and dispensing of the components used to manufacture concrete. According to one embodiment, the components are preferably weighed or measured with an accuracy of about .+-.2.0%, more preferably with an accuracy of about .+-.1.0%, and most preferably with an accuracy of about .+-.0.5%. The amount of water included in the concrete composition is carefully controlled so that it does not significantly change from the time the composition is first made within the concrete truck and when it is used at the job site. In order to prevent decreases in actual strength due to human error, on-site slump adjustments can be made to wet concrete compositions through the use of special admixtures instead of by increasing the water content.

In order to account for all water inputs, the moisture content of the solid components (e.g., hydraulic cement and aggregates) can be continuously monitored using moistur