<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-11-25</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000792987</issuerCik>
        <issuerName>ASTEC INDUSTRIES INC</issuerName>
        <issuerTradingSymbol>ASTE</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001084492</rptOwnerCik>
            <rptOwnerName>SANSOM WILLIAM B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>MARTIN MARIETTA MATERIALS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>2710 WYCLIFF ROAD</rptOwnerStreet2>
            <rptOwnerCity>RALEIGH</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>27607</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

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                <value>Common Stock</value>
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                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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    </nonDerivativeTable>

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            </transactionAmounts>
            <exerciseDate>
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            </exerciseDate>
            <expirationDate>
                <value>2014-03-18</value>
            </expirationDate>
            <underlyingSecurity>
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                </underlyingSecurityTitle>
                <underlyingSecurityShares>
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                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
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                <directOrIndirectOwnership>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
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            </conversionOrExercisePrice>
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                <value>2013-11-25</value>
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            <deemedExecutionDate></deemedExecutionDate>
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                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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            <exerciseDate>
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            <expirationDate>
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                </underlyingSecurityShares>
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            <expirationDate>
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                <underlyingSecurityTitle>
                    <value>Common Stock</value>
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            <exerciseDate>
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            <expirationDate>
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        <derivativeHolding>
            <securityTitle>
                <value>Stock Options</value>
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                <value>34.43</value>
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            <exerciseDate>
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            <expirationDate>
                <value>2016-03-16</value>
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        <derivativeHolding>
            <securityTitle>
                <value>Stock Optiions</value>
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                    <value>D</value>
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                <value>Stock Options</value>
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        </derivativeHolding>
    </derivativeTable>

    <footnotes></footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Robert Taylor, attorney in fact for William B. Sansom</signatureName>
        <signatureDate>2013-12-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
