<PAGE>

                                                                     EXHIBIT 4.5

                               THIRD AMENDMENT TO
                        Amended and Restated Credit Agreement
                        -------------------------------------


          This THIRD AMENDMENT TO AMENDED AND RESTATED CREDIT AGREEMENT (this
"Third Amendment"), effective as of March 31, 2001, is entered into by and among
U.S. CONCRETE, INC., a Delaware corporation, (the "Company"), the Guarantors
signatory hereto under the caption "Guarantors" (together with each other Person
who becomes a Guarantor, collectively, the "Guarantors"), the Lenders signatory
hereto under the caption "Lenders" (together with each other Person who becomes
a Lender, collectively, the "Lenders") and THE CHASE MANHATTAN BANK, a New York
banking corporation, successor-in-interest by merger to Chase Bank of Texas,
National Association, as administrative agent for the other Lenders (in such
capacity, together with any other Person who becomes the administrative agent,
the "Administrative Agent"), Bankers Trust Company, as syndication agent, First
Union National Bank, as documentation agent, and Bank One, Texas, NA, Branch
Banking & Trust Company, Credit Lyonnais New York Branch and The Bank of Nova
Scotia, collectively as co-managing agents for the Lenders.

                             PRELIMINARY STATEMENT

  WHEREAS, the Company, the Guarantors, the Lenders, the Administrative Agent,
the syndication agent, the documentation agent and the co-managing agents have
entered into that certain Amended and Restated Credit Agreement dated as of
February 9, 2000 (the "Original Credit Agreement") under the terms of which the
Lenders agreed to make Revolving Credit Loans to the Company in an amount not
exceeding $200,000,000.00; and

  WHEREAS, the Company, the Guarantors, the Lenders, the Administrative Agent,
the syndication agent, the documentation agent and the co-managing agents have
amended the Original Credit Agreement pursuant to that certain First Amendment
to Amended and Restated Credit Agreement dated as of July 7, 2000 (the "First
Amendment"); and

  WHEREAS, the Company, the Guarantors, the Lenders, the Administrative Agent,
the syndication agent, the documentation agent and the co-managing agents have
amended the Original Credit Agreement pursuant to that certain Second Amendment
to Amended and Restated Credit Agreement dated as of September 30, 2000 (the
"Second Amendment")(the Original Credit Agreement, as amended by the First
Amendment and the Second Amendment and as may be further amended, extended,
supplemented or restated from time to time, the "Credit Agreement"); and

  WHEREAS, the Company has requested the Lenders and the Administrative Agent to
further amend certain terms of the Credit Agreement; and

  WHEREAS, the Lenders and the Administrative Agent have agreed to do so to the
extent reflected in this Third Amendment, provided that each of the Company and
the Guarantors ratifies and confirms all of its respective obligations under the
Credit Agreement and the Loan Documents.
<PAGE>

  NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration and the mutual benefits, covenants and agreements herein
expressed, the receipt and sufficiency of which are hereby acknowledged, the
parties hereby agree as follows:

  1. Defined Terms. All capitalized terms used in this Third Amendment and not
otherwise defined herein shall have the respective meanings ascribed to such
terms in the Credit Agreement.

  2. Amendment to Section 6.08(a). Section 6.08(a) of the Credit Agreement is
hereby deleted in its entirety and replaced by the following:

     "(a)  Fixed Charge Coverage Ratio. The Borrower will not at any time permit
     the ratio of (i) EBITDA calculated on a rolling four (4) quarter basis
     (excluding any EBITDA computed pursuant to clause (b) of the definition of
     EBITDA) minus cash federal, state and local income and franchise taxes
     actually paid during such period, to (ii) cash interest expense, actually
     paid during such period (including the interest expense portion of any
     payments on Capitalized Lease Obligations but net of cash interest income
     actually received during such period) plus Maintenance Capital Expenditures
     for said period, to be less than (y) for the period ending March 31, 2001
     and the period ending June 30, 2001, 1.5 to 1.0; (z) for the period ending
     September 30, 2001 and thereafter during the term hereof, 1.75 to 1.0.".

  3. Amendment to Section 6.11. Section 6.11 of the Credit Agreement is hereby
deleted in its entirety and is replaced by the following:

     "Section 6.11.  Limitation on Acquisitions.  The Borrower will not, and
     will not permit any Subsidiary to, acquire (i) any securities of, or
     outstanding ownership interests in, any Person, or (ii) all or
     substantially all of the assets of any Person, whether through purchase of
     assets, merger or otherwise, without the prior written consent of the
     Required Lenders; provided, however, that the Borrower and/or any
     Subsidiary shall be entitled to acquire the securities of, outstanding
     ownership interests in, or assets of (x) any wholly owned Guarantor listed
     on the signature page of this Third Amendment, (y) any wholly owned
     Guarantor acquired, with the prior written consent of the Required Lenders,
     after the date hereof, or (z) any entity created by the merger, conversion,
     recapitalization or other restructuring of any entity described in (x) or
     (y) above, provided that after such merger, conversion, recapitalization or
     other restructuring, all or substantially all of such entity's assets
     consist of the securities of, outstanding ownership interests in, or assets
     of the entities described in (x) and (y) above.".

  4. Ratification. Each of the Company, as to itself and each Guarantor, and
each Guarantor, as to itself, hereby ratifies all of its respective obligations
under the Credit Agreement (including the Guaranty contained in Article X
thereof) and each of the Loan Documents to which it is a party, and agrees and
acknowledges that the Credit Agreement and each of the Loan Documents to which
it is a party remains in full force and effect and shall continue in full force
and effect as amended and modified by this Third Amendment. Nothing in this
Third Amendment extinguishes, novates or releases any right, claim, lien,
security interest or entitlement of any of the Lenders or the Administrative
Agent created by or contained in any of such documents nor is the Company or any


                                       2
<PAGE>

Guarantor released from any covenant, warranty or obligation created by or
contained therein or herein.

  5.  Representations and Warranties. Each of the Company, as to itself and each
Guarantor, and each Guarantor, as to itself, hereby represents and warrants to
the Administrative Agent and the Lenders that (a) this Third Amendment has been
duly executed and delivered on behalf of the Company and such Guarantor, subject
to applicable bankruptcy, insolvency, fraudulent transfer, reorganization,
moratorium or other laws affecting creditors' rights generally and subject to
general principles of equity, regardless of whether considered in a proceeding
in equity or at law, (b) this Third Amendment constitutes a valid and legally
binding agreement enforceable against the Company or such Guarantor, as the case
may be, in accordance with its terms, subject to applicable bankruptcy,
insolvency, fraudulent transfer, reorganization, moratorium or other laws
affecting creditors' rights generally and subject to general principles of
equity, regardless of whether considered in a proceeding in equity or at law,
(c) the representations and warranties contained in the Credit Agreement and the
Loan Documents shall be true and correct on and as of the date of each Borrowing
and the date of issuance, amendment, renewal or extension of each Letter of
Credit, as applicable, except to the extent such representations and warranties
relate to a prior date or, after prior notice to the Administrative Agent, are
untrue or incorrect as a result of transactions permitted by the Loan Documents,
(d) no Default exists under the Credit Agreement (as amended hereby) or under
any other Loan Document and (e) the execution, delivery and performance of this
Third Amendment has been duly authorized by the Company and each Guarantor.

  6.  Conditions to Effectiveness. This Third Amendment shall be effective upon
(i) the execution hereof by the Guarantors, the Borrower and the Required
Lenders and delivery to the Administrative Agent and receipt by the
Administrative Agent of this Third Amendment executed by all such parties, and
(ii) receipt by the Administrative Agent of an amendment fee payable by the
Company to the Administrative Agent for the pro rata benefit of the Lenders of
0.10% of the total Commitments.

  7.  Counterparts.  This Third Amendment may be signed in any
number of counterparts, which may be delivered in original or facsimile form
each of which shall be construed as an original, but all of which together shall
constitute one and the same instrument.

  8.  Governing Law. THIS THIRD AMENDMENT, THE CREDIT AGREEMENT,
ALL NOTES, THE OTHER LOAN DOCUMENTS AND ALL OTHER DOCUMENTS EXECUTED IN
CONNECTION HEREWITH SHALL BE DEEMED TO BE CONTRACTS AND AGREEMENTS UNDER THE
LAWS OF THE STATE OF TEXAS AND OF THE UNITED STATES OF AMERICA AND FOR ALL
PURPOSES SHALL BE CONSTRUED IN ACCORDANCE WITH, AND GOVERNED BY, THE LAWS OF
TEXAS AND OF THE UNITED STATES.

  9.  Final Agreement of the Parties.  THIS THIRD AMENDMENT AND
THE CREDIT AGREEMENT AND THE OTHER LOAN DOCUMENTS REPRESENT THE FINAL AGREEMENT
BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES.  THERE ARE NO
UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.


                                       3
<PAGE>

  IN WITNESS WHEREOF, the parties hereto have caused this Third Amendment to be
executed by their respective officers thereunto duly authorized as of the date
first above written.

                         COMPANY:

                              U.S. CONCRETE



                              By: /s/ Michael W. Harlan
                                  ---------------------
                                  Michael W. Harlan
                                  Senior Vice President


                                       4

<PAGE>

                       GUARANTORS:

                       AFTM Corporation, a Michigan corporation
                       American Concrete Products, Inc., a California
                         corporation
                       Atlas-Tuck Concrete, Inc., an Oklahoma corporation
                       B.W.B., Inc. of Michigan, a Delaware corporation
                       Baer Concrete, Inc., a New Jersey corporation
                       Beall Concrete Enterprises, Ltd., a Texas limited
                         partnership
                       Beall Industries, Inc., a Texas corporation
                       Beall Management, Inc., a Texas corporation
                       Carrier Excavation and Foundation Company, a Delaware
                         corporation
                       Central Concrete Supply Co., Inc., a California
                         corporation
                       Central Precast Concrete, Inc., a California corporation
                       Concrete XX Acquisition, Inc., a Delaware corporation
                       Corden, Inc., a Michigan corporation
                       Cornillie Fuel & Supply, Inc., a Michigan corporation
                       Cornillie Leasing, Inc., a Michigan corporation
                       Dencor, Inc., a Michigan corporation
                       DYNA, Inc., a Delaware corporation
                       E.B. Metzen, Inc., a Michigan corporation
                       Fendt Transit Mix, Inc., a Michigan corporation
                       Hunter Equipment Company, a Michigan corporation
                       Olive Branch Ready Mix, Inc., a Delaware corporation
                       Opportunity Concrete Corporation, a District of Columbia
                         corporation
                       Premix Concrete Corp., a Delaware corporation
                       Ready Mix Concrete Company of Knoxville, a Delaware
                         corporation
                       San Diego Precast Concrete, Inc., a Delaware corporation
                       Sierra Precast, Inc., a California corporation
                       Stokes Transit Mix, Inc., an Oklahoma corporation
                       Superior Materials Company, Inc., a Delaware corporation
                       Superior Redi-Mix, Inc., a Michigan corporation
                       USC GP, Inc., a Delaware corporation
                       USC Management Co., LP, a Texas limited partnership
                       USC Midsouth, Inc., a Delaware corporation



                       By: /s/ Michael W. Harlan
                           ---------------------
                           Michael W. Harlan
                           Vice President


                                       5

<PAGE>

                         Administrative Agent/Lender:
                         ---------------------------

                              THE CHASE MANHATTAN BANK



                              By:/s/ James R. Dolphin
                                 --------------------
                                 James R. Dolphin
                                 Senior Vice President


                                       6
<PAGE>

                         Syndication Agent/Lender:
                         ------------------------

                              BANKERS TRUST COMPANY



                              By: /s/ Susan L. LeFevre
                                  --------------------
                                  Name:  Susan L. LeFevre
                                  Title: Director


                                       7
<PAGE>

                         Documentation Agent/Lender:
                         --------------------------

                              FIRST UNION NATIONAL BANK



                              By: /s/ J. Andrew Phelps
                                  --------------------
                                  Name:  J. Andrew Phelps
                                  Title: Vice President


                                       8
<PAGE>

                          Lender:
                          ------

                              BANK OF AMERICA, N.A.,



                              By: /s/ William B. Borus
                                  --------------------
                                  Name:  William B. Borus
                                  Title: Senior Vice President


                                       9
<PAGE>

                         Co-Managing Agent/Lender:
                         ------------------------

                              BANK ONE, N.A. (formerly known as
                              Bank One, Texas, N.A.)



                              By: /s/ John J. Zollinger, IV
                                  -------------------------
                                  Name:  John J. Zollinger, IV
                                  Title: Associate Director


                                       10
<PAGE>

                         Co-Managing Agent/Lender:
                         ------------------------

                              CREDIT LYONNAIS
                              NEW YORK BRANCH



                              By: /s/ Attila Koc
                                  --------------
                                  Name:  Attila Koc
                                  Title: Senior Vice President



                                      11
<PAGE>

                         Co-Managing Agent/Lender:
                         ------------------------

                              THE BANK OF NOVA SCOTIA



                              By: /s/ M. D. Smith
                                  ---------------
                                  Name:  M. D. Smith
                                  Title: Agent


                                      12
<PAGE>

                         Co-Managing Agent/Lender:
                         ------------------------

                              BRANCH BANKING & TRUST COMPANY



                                    By: /s/ Cory Boyte
                                        --------------
                                        Name:  Cory Boyte
                                        Title: Vice President


                                      13
<PAGE>

                              Lender:
                              ------

                                   COMERICA BANK



                                   By:   /s/ Gerald R. Finney, Jr.
                                         -------------------------
                                   Name:   Gerald R. Finney, Jr.
                                   Title:  Vice President


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