INVESTIGATION OF METHODS FOR REMOVING STAINS FROM MORTAR AND CONCRETE

Transcription

1 TA7 W34m no. C-68-8 c.4,,,, "\.J Property of t.~ MISCELLANEOUS PAPER C-68-8 INVESTIGATION OF METHODS FOR REMOVING STAINS FROM MORTAR AND CONCRETE by C. F. Derrington R. L. Stowe W. G. Mier October 968 Sponsored by Office, Chief of Engineers U. S. Army Conducted by U. S. Army Engineer Waterways Experiment Station CORPS OF ENGINEERS Vicksburg, Mississippi I~ DOCUMENT HAS BEEN APPROVED FOR PUBLIC RELEASE. ~Y '\ND SALE; ITS DISTRIBUTION IS UNLIMITED.~,,..~ _..,

2 MISCELLANEOUS PAPER C-68-8 /A W3M () 0, c ~6 g'.. g C. _ '-f INVESTIGATION OF METHODS FOR REMOVING STAINS FROM MORTAR AND CONCRETE by C. F. Derrington R. L. Stowe W. G. Mier October 968 Sponsored by Office, Chief of Engineers U. S. Army ARMY MRC VICKSBURG. MISS. Conducted by U. S. Army Engineer Waterways Experiment Station CORPS OF ENGINEERS Vicksburg, Mississippi THIS DOCUMENT HAS BEEN APPROVED FOR PUBLIC RELEASE AND SALE; ITS DISTRIBUTION IS UNLIMITED

3 FOREWORD This report was prepared as part of Subproject , "Stain Remova," of ES Item 620, "Forming, Finishing, and Curing Concrete." Authority for the work was provided by the second indorsement dated 3 November 964 to etter from the Office, Chief of Engineers, dated 2 October 964, subject, "Project Pan for Investigation of Methods of Remova of Stains from Concrete Surfaces." The work reported herein was conducted during the period November 964-November 967. The iterature search was made by Mr. Wiiam G. Mier. The aboratory work was conducted by Messrs. Wiiam G. Mier and Richard L. Stowe. This report was written by Mrs. C. F. Derrington and Messrs. Stowe and Mier under the supervision of Messrs. Thomas B. Kennedy, Bryant Mather, R. V. Tye, James M. Poatty, Leonard Pepper, and W. 0. Tynes, a of the U.S. Army Engineer Waterways Experiment Station (WES) Concrete Division. Directors of the WES during the aboratory: work were CDL- Aex_ G_._ Sutton, Jr., CE, and COL John R. Oswat, Jr., CE. The Directors during the compiation and pubication of this report were COL John R. Oswat, Jr., CE, and COL Levi A. Brown, CE. Technica Director was Mr. J, B. Tiffany. iii

4 CONTENTS FOREWORD CONVERSION FACTORS, BRITISH TO METRIC UNITS OF MEASUREMENT SUMMARY PART I: INTRODUCTION. PART II: LITERATURE SEARCH. Mechanica Methods of Removing Stains from Concrete. Chemica Methods of Removing Stains from Concrete.. Genera Procedure and Precautions.... PART III: EVALUATION OF STAIN REMOVAL METHODS USING MORTAR SPECIMENS PART IV: PART V: Iron Stains Lubricating Oi and Asphat Stains.... EVALUATION OF STAIN REMOVAL METHODS ON CONCRETE SPECIMENS.... Preparation of Concrete Specimens. Iron Stain Lubricating Oi and Asphat Stains CONCLUSIONS AND RECOMMENDATIONS LITERATURE CITED Page iii vii ix v

5 CONVERSION FACTORS, BRITISH TO METRIC UNITS OF MEASUREMENT British units of measurement used in this report can be converted to metric uni ts as foows : Mutipy inches feet square feet gaons (u. s.) ounces pounds pounds per square inch Fahrenheit degrees By o /9 To Obtain centimeters meters square meters cubic meters grams kiograms kiograms per square centimeter Cesius or Kevin degrees* * To obtain Cesius (c) temperature readings from Fahrenheit (F) readings, use the foowing formua: C = (5/9)(F - 32). To obtain Kevin (K) readings, use: K = (5/9)(F - 32) vii

6 SUMMARY This investigation consisted of three parts: (a) a iterature search to acquire information on the types of stains that can be expected and methods of remova; (b) evauation of methods of removing stains from mortar specimens; and (c) evauation of promising stain remova methods on concrete specimens. The iterature search indicated that the types of troubesome stains most ikey to be found on concrete surfaces are those caused by iron, used ubricating ois, and cutback asphats. Severa chemica and mechanica methods for their remova are outined herein. Mortar specimens were made in the aboratory and stained to a mid or severe degree with a soution of iron choride, ubricating oi, or asphat. The most effective remova techniques for iron stains were sandbasting, appication of an oxaic acid soution, and appication of a sodium citrate-sodium hydrosufite paste. Oi and asphat stains were not competey removed by any of the methods, but the benzene-cac03 paste was the most effective remova method of those used. Concrete specimens were aso made, and were severey stained with iron, oi, and asphat. The most effective remova methods for the iron stains were sandbasting and appication of a sodium citrate-sodium hydrosufite paste; the oi stains were best removed by the sandbasting and the benzene-cac03 paste methods. The asphat stains were not satisfactoriy removed by any of the techniques that wera tri ea. ix

7 INVESTIGATION OF METHODS FOR REMOVING STAINS FROM MORTAR AND CONCRETE PART I: INTRODUCTION. One of the most prevaent types of stain found on concrete is caused by deposits eft from curing water. Prior to 963, the Standard Guide Specifications for Concrete controed this type of staining by specifying that water used for curing concrete be nonstaining. In 963, paragraph 5(b) of reference was revised, eiminating this requirement. However, this revised edition does provide that there be no permanent staining of surfaces where appearance is important. For these surfaces, the contractor has the option of using nonstaining water or ceaning the surfaces after competion of moist curing. 2. Athough stains produced by water are the most common, other stains often occur during construction. The investigation reported herein was initiated for the purpose of evauating the efficiency and acceptabiity of methods of removing various types of stains from mortar and concrete. The investigation was divided into three phases, as foows: (a) a iterature search to determine the types of stains that can be expected and methods for removing these stains, (b) evauation of methods of removing stains using sma mortar specimens, and (c) evauation of the more promising remova :method& on arger concrete_ specimens_,_ The_ three phases have been competed, and the resuts are reported herein.

8 PART II: LITERATURE SEARCH 3. A search was made of the iterature to determine the most prevaent types of stain found on concrete caused by materias that are normay used during construction and the chemica and mechanica methods used to remove these stains. It was found that stains on concrete may be caused by iron, oi, asphat, copper, bronze, auminum, wet or dry paint, coffee, iodine, perspiration, urine, ink, tobacco, fire, rotten wood, or other misceaneous materias. 4. Remova of stains from concrete may invove either chemica or mechanica methods. The type of stain to be removed, avaiabiity of chemicas or suitabe equipment, cost of overa ceaning operation, and effectiveness of stain remova wi determine the particuar method seected for a particuar job, The penetration of stains into concrete is dependent on the porosity of the concrete surface and the viscosity of the staining materia. Poutices or bandages, rather than a surface wash, are required to remove stains that have penetrated into concrete. Poutices are made by mixing active chemicas with a fine inert powder to a pasty consistency and appying in a thick ayer to the stained area. Bandages are made by soaking ayers of cotton batting, coth, or paper toweing in a chemica soution and appying the wet materia to the stain. Often -these _tj:'eatmen_ts _need _r_epeating to remove stubborn stains. Mechanica Methods of Removing Stains from Concrete 5, The mechanica methods of ceaning concrete incude sandbasting, steam ceaning, water jet, and water surry jet. Sandbasting usuay ceans effectivey. It invoves ejecting sand with compressed air through a nozze against the concrete surface. The sand removes the stain by abrading the concrete surface. The type of sandbasting equipment, other materias needed, and number of personne required to remove stains are dictated by the type and accessibiity of the structure and the size of the area to be ceaned. The equipment and procedures described in the iterature have been found to be satisfactory. 2 2

9 6. High-pressure steam 2 is an effective and reativey economica method of ceaning concrete. The steam is projected at high veocity on a concrete surface, and grime, dirt, soot, and other extraneous matter are dissoved and disodged and ater fushed down with a rinsing hose. Akaies such as sodium carbonate, sodium bicarbonate, and trisodium phosphate are sometimes added to the ceaning water to hasten the ceaning action. If these sats are added to the ceaning water, it is necessary to rinse the surface we with cear water to remove the sats so that efforescence wi not ater appear on the surface. Steam ceaning does not harm concrete surfaces; however, it is most effective for genera ceaning and not for specific stain remova. 7, The water jet method is sometimes used for ceaning masonry and removing stains. This method invoves directing water under pressure (approximatey 00 psi) onto a concrete surface by means of a hose equipped with a nozze having a very narrow opening. The water jet method can deiver an extremey fine spray of water at a high veocity. The veocity with which the water is directed against the surface, not the voume of discharge, is significant in determining the effectiveness of the method. Fushing a surface with cear water prior to and after the use of the water jet wi aid in the remova of stain. The type of pressure hoses, the ength of water suppy hoses, the amount of scaffoding, and the number of personne needed are dictated by the job conditions. 8. The addition of fines, i.e. sand, fy ash, etc., to a water jet system by forming a surry of these materias in water wi increase the abrasive action on the concrete and can be an effective means of removing stains. The principes and procedures foowed in the water jet method are essentiay the same for this method. The type, size, and quantity of the added fines determine the equipment needed to maintain a surry and to produce the desired pressure. Chemica Methods of Removing Stains from Concrete 9, Most of the stains caused by specific substances are removed by various specified methods invoving the appication of specific chemicas. 3

10 The various stains most often encountered on concrete and the methods of removing them are described in the foowing paragraphs. Iron stains 0. The most common stain found on concrete is iron stain, which is usuay caused by excessive a.mounts of iron sats deposited from the curing water or by weathering of unprotected structura stee. Usuay this type of stain is confined to the surface if the concrete is not permitted to dry appreciaby before appication of the curing water. Surface condition, ength of exposure to heat and ight, the concentration of iron sats in the curing water, and the rate of fow of the curing water are factors that determine the severity of the stain that is produced. Rust from structura stee produces ocaized areas of stain. These stains may become severe because the concrete is usuay dry, and penetration of the surface wi occur. The treatment necessary to remove iron stains is, of course, dependent upon the severity and penetration of the stain. The foowing chemica methods of iron stain remova are recommended.3,4,5. Surface stains. The surface is mopped with a soution consisting of b* of oxaic acid in ga of water. After 2 or 3 hr, the treated surface is scrubbed we with stiff brushes and cear water. The surface is then fushed with cear water unti a traces of the acid have been removed. The stained surface shoud be saturated with water before appication of the acid soution so that the acid wi not migrate too deepy into the concrete pores. 2. Deeper stains. a. Treatment with sodium citrate, water, gycerin, and cacium carbonate. One part of sodium citrate is dissoved in six parts of water that has been mixed with seven parts of gycerin; sufficient Caco 3 is then added and mixed we to form a paste just stiff enough to adhere adequatey to the surface. The paste is appied to the stained surface with a trowe or putty knife to a thickness of' about /4 in. and * A tabe of factors for converting British units of measurement to metric units is presented on page vii. 4

11 aowed to remain for at east two days. At the end of this period, the poutice is scraped off, and the concrete surface is rinsed thoroughy with cear water. This treatment produces no injurious effects and can be repeated for stubborn stains. b. Mixture of ammonium citrate, water, gycerin, and cacium carbonate. Treatment of stains and the method of mixing the chemicas are identica with those described in subparagraph a above. However, the mixture shoud be removed from the stained area sooner (perhaps after one day), since the ammonium citrate produces resuts more quicky but may cause the concrete surface to become sighty etched. c. Sodium hydrosufite, sodium citrate, water, and Caco 3 First, the surface shoud be soaked with a soution of one part sodium citrate and six parts water. Soaking can be done by dipping white coth or cotton batting into this soution and pacing the coth over the stain for 0 or 5 min. On horizonta surfaces, after the coth has been removed, crystas of sodium hydrosufite are sprinked over the stained area, moistened with water, and covered with a stiff paste made of CaC03 and water. On vertica surfaces, the Caco 3 paste is appied with a trowe after the sodium citrate treatment; then a ayer of the sodium hydrosufite is sprinked onto the paste and moistened sighty. The poutice is removed after hr, and the surface is rinsed with cear water. If the mixture is eft onger than hr, a back stain may deveop. If the iron stain persists, treatment shoud be repeated, using fresh materias. Lubricating oi stains (petroeum) 3. Most horizonta concrete sabs are vunerabe to ubricating oi stains. If the oi is removed immediatey, there is itte danger of staining. Powders such as hydrated ime, Fuer's earth, whiting, or dry portand cement are effective botting agents. If the oi is aowed to 5

12 penetrate into the pores of the concrete and an accumuation of dirt buids up, remova becomes more difficut and may require both mechanica and chemica remova methods. 4. Severa methods of oi stain remova are suggested,2,4,5,6 some being mo~e efficacious and practica than others. The foowing methods have been recommended for remova of ubricating ois. a. Trisodium phosphate-cac03 mixture. One pound of trisodium phosphate is dissoved in ga of water, and sufficient CaC03 is added to make a stiff paste. A ayer of the paste, approximatey /2 in. thick, is appied to the stained surface and aowed to remain unti it dries (approximatey 24 hr). The paste is then removed, and the surface is rinsed with cear water. b. NaOH-CaC03 mixture. A poutice is made by adding Caco 3 to a 5 percent NaOH soution. This mixture is appied in the same manner as described in subparagraph!!:. above. c. Benzene-CaC03 paste. Sufficient Caco 3 is added to benzene to form a stiff paste. The paste is appied with a trowe or by other suitabe means and aowed to remain in position for hr after the sovent has evaporated. After remova of the paste, the surface is rinsed with cear water. d. Acetone-amy acetate. First, a surface oi is removed by scrubbing with a strong soap containing trisodium phosphate, or with a scouring powder. Then a bandage saturated with equa parts of acetone and amy acetate is appied to the stained area and covered with a heated concrete sab or a pane of gass. The heated concrete sab wi draw the dissoved oi out of the stained area. The gass pane wi force the dissoved oi deeper into the concrete and out of sight. e. Asbestos-amy acetate. This procedure is simiar to the method described in subparagraph i above, except that the stained area is covered with a /4-in.-thick mat of asbestos 6

13 fiber that is saturated with amy acetate. A heated concrete sab paced on top of the saturated asbestos draws the stained oi from the concrete. f. Methy choroform. White cotton fanne is saturated with,, -trichoroethane (methy choroform) and paced over the stained area. The area is then covered with either a sheet of gass or a sab of concrete, depending upon whether remova is to be accompished by driving the oi into the concrete or drawing it out. Linseed oi stains 5. Linseed oi, if aowed to remain on concrete unti it oxidizes and forms a resinous substance, requires a beaching treatment. Before treatment, excess oi shoud be removed by botting the surface with hydrated ime, Fuer's earth, or CaC03. After this initia treatment, two effective stain remova procedures are as foows.2, 4,5,6 a. Trisodium phosphate, sodium perborate, cacium carbonate, and soap. One part trisodium phosphate, one part sodium perborate, and three parts of Caco 3 are mixed thoroughy, and a strong, hot soution of soap is added to the mixture unti a paste is formed. The stain is covered with a /8- in. ayer of paste. The paste is removed when thoroughy dry, and the surface is scrubbed with cear water. This method is stateii to be the most effective- for remova- of inseed oi. b. Hydrogen peroxide-ammonia water. This second method is somewhat simper but ess effective than the one described in subparagraph!!. above. Therefore, it shoud be used when the stain is not severe. A bandage of cotton is saturated with hydrogen peroxide and paced over the stain. The beaching action is acceerated by moistening another coth with ammonia and pacing it over the cotton bandage. This operation can be repeated if necessary. Asphat stains 6. The stains produced on concrete by asphat are normay the most 7

14 difficut to remove, especiay if the asphat has been aowed to penetrate very far into the concrete. The three types of asphat encountered are usuay petroeum, emusified, or cutback. The type of asphat greaty infuences the degree of penetration and the amount of staining produced. The minimum degree of penetration is usuay found with petroeum asphats, the maximum penetration with cutback asphats, and a degree of penetration somewhere between these two with the emusified asphats. The characteristics of the materias used to cut back asphats, e.g., natura and synthetic resins and ois or aromatic and/or aiphatic sovents, have a definite effect on the degree of penetration and the method of remova to be used. Carefu and vigorous mechanica preceaning by scraping and scrubbing is essentia before attempting to treat an asphat-stained surface chemicay. The foowing methods are used for removing asphat stains from concrete. 2,4,6 a. Petroeum asphat stains. Petroeum asphat stains are satisfactoriy removed by cooing with ice unti britte. The embritted asphat is chipped off the concrete surface with a chise, foowed by scraping to remove most of the adherent residue. The surface is then scrubbed with abrasive powder and washed with water. Ordinary ice is more effective than dry ice in the cooing operation. This method is tedious and time-consuming and not economica or practica for arge areas. b. Emusified asphat stains. Emusified asphat stains are satisfactoriy removed by scrubbing the stained area with scouring powder and water. Sovents shoud not be used in either iquid or paste form, since they woud increase penetration to such a degree that remova woud be impossibe. c. Cutback asphat stains. Cutback asphat stains are neary impossibe to remove competey. Repeated appications of a benzo paste (benzo-diatomaceous earth) foowed by scrubbing with a scouring powder and water reduce the intensity of the stain, but wi not remove it competey. 8

15 A second method suggested for remova of cutback asphat stains invoves treatment of the surface with a soution made of equa parts of dimethy sufoxide and water. soution is aowed to stay in contact with the stained areas for hr. Copper and bronze stains The Then the area is vigorousy scrubbed with an excess of the soution, using a moderatey stiff briste brush, and rinsed with cear water. 7. Copper and bronze stains are usuay caused by water carrying the oxidation of unprotected meta over concrete surfaces. The characteristic coor of these stains is usuay green, but may be brown. These stains are readiy removed by the foowing method:2,3,4,5,6 One part ammonium choride and four parts of powdered tac or diatomaceous earth are mixed dry and then made into a paste with ammonia water. This paste is appied in a /8- to /4-in.-thick ayer over the stained area and aowed to dry. After drying, the paste is removed and the surface is thoroughy rinsed with cear water. Auminum stains 8. Auminum stains have become more common with the increased use of auminum in construction. The stains appear as whitish deposits on concrete and may be easiy removed by scrubbing with a 0 to 20 percent hydrochoric (muriatic) acid soution. 2, 3, 4,5, 6 Surfaces treated with hydrochoric acid must be thoroughy rinsed with ~e-ar-water-tu-preventpenetration of the dissoved sats into the pores of the concrete. Paint stains 9. Freshy spied paint shoud be soaked up with a cean, absorbent coth immediatey. hep prevent the stain from spreading. Botting and sponging, rather than wiping, wi vigorousy scrubbed with scouring powder and water. The stained area shoud then be Paint removers or sovents shoud never be used on spied paint or on fims ess than three days od, since they tend to increase the penetration of the paint into the concrete surface. 20. Paint removers have been found satisfactory for the remova of dried oi paints, enames, varnishes, sheacs, and gue sizings. The 9

16 paint remover is appied to the stained area unti the paint can be scraped off with a putty knife or fushed off with water. Then the area is scrubbed with scouring powder and water and fushed with cear water. Efficient paint removers incude the foowing: 2,4, 6 (a) a noncombustibe, ow-toxicity paint remover; (b) 2 b of trisodium phosphate in ga of hot water; (c) 2-/2 b of caustic soda in ga of hot water; (d) equa parts of dimethy sufoxide and sovents such as methyene choride, benzene, or xyene; (e) equa parts of soda ash and quickime mixed with sufficient water to form a paste; and (f) one part NaOH dissoved in three parts water and added to one part minera oi, and this stirred, emusified mixture is then mixed with one part sawdust or other inert materia. Methyene choride and dimethy sufoxide are midy toxic, so proper precaution shoud be exercised in their use. If the oi paint is very thick and hard, sandbasting may be necessary to remove it. Paint fims can be burned off, but this method is not recommended because of the fire hazard. Ink stains 2. A effective ink stain remova techniques are based on beaching, athough different inks require different beaching treatments. The beach can be appied by fooding the area with the beaching soution, saturating pieces of cean white coth with the beach and pressing them against the surface by means of pate gass or cean wood, or appying a paste made from the beach and powdered tac. Some of the more effective -beadres --re-c-ommended for ink stain remova-i2,3,4,5 are: (a) strong sodium perborate water soution mixed with caco 3 to desired consistency; (b) Javee water (sodium hypochorite); (c) ammonia water; (d) paste of chorinated ime and Caco 3 ; (e) equa parts of chorinated ime, cacium hypochorite, and Caco 3 ; and (f) potassium hypochorite and potassium choride. If a brown residue remains after any of these treatments, it can be removed by washing the area with an oxaic acid soution (described in paragraph ). Thorough rinsing with cear water shoud foow the use of a these beaches. Iodine stains 22. Iodine stains graduay disappear of their own accord; however, remova of these stains can be hastened by appying a mixture of acoho 0

17 with either Caco 3 or tacum powder. A~er the paste has been aowed to dry, it is scraped off, and the surface is washed with cear water. 2 '3,5 Coffee stains 23. Coffee stains can be removed by appying a coth that has been saturated in any of the three foowing soutions: (a) one part gycerin and four parts water by voume, (b) Javee water, or (c) a mixture of chorinated ime and trisodium phosphate as described for removing tobacco stains. 2 ' 3, 4,5 Tobacco, fire, rotten wood, urine, and perspiration stains 24. The stains in this group are usuay removed by beaching. 2 '3, 4,5 An effective beach for these stains is made by mixing 2 oz of chorinated ime with water to form a paste. This paste is then put in a 2-ga container containing a soution of 2 b of trisodium phosphate dissoved in ga of hot water. Additiona water is added, if needed, to fi the 2- ga container. This mixture is stirred, covered, and aowed to stand unti the precipitate settes. The decanted cear iquid is a strong corrosive beach, and is appied to the stains in this group either with a coth that has been saturated with the beach or as a poutice made of the beach and tac. Treated areas shoud be thoroughy fushed with cear water after the remova of the poutice or bandage. Genera discoorations of concrete. 25. There are severa ractors tnat determne ~ne surr-ace appearance If these factors are not cosey controed, certain discoorations such as dark spots, ight spots, and efforescence may occur. These discoorations5 can be caused by uneven water-cement ratio, nonuniform curing, admixtures, coor and composition of the cement, subgrade, or finishing practices. Dark spots can o~en be removed with a singe washdown of water; but if the concrete contains cacium choride, severa washings may be necessary. Light spots are usuay more difficut to remove and require either a treatment with a 0 percent sodium hydroxide soution or the appication of dia.mmonium citrate crystas foowed by thorough rinsing with water. The most effective treatment for efforescence is proonged fushing with water immediatey after the efforescence

18 appears and scrubbing with a stiff brush. If the efforescence cannot be treated immediatey, it may be necessary to wash with a very weak soution of phosphoric acid or acetic acid for effective remova. A treatments for discooration are more effective if the concrete surfaces are washed soon after the spots appear. Genera Procedure and Precautions 26. The techniques described in the preceding paragraphs are basic for the materias causing the stains. In actua practice or under fied conditions, many variabes may be invoved. It is, therefore, advisabe to study the stain carefuy and to pan the ceaning method before actuay starting to remove the stain. The best approach is to prepare a sma tria quantity of the removing agent and appy it at the most inconspicuous point to assess its vaue. The composition or strength can then be modified appropriatey. 27. A of the chemicas mentioned above are avaiabe commerciay, and under norma conditions can be used both indoors and outdoors if precautions regarding fammabiity and toxicity are observed. Two eementary precautions that need to be observed are: (a) wash hands thoroughy after using the chemicas, and (b) if f'uming shoud occur, provide for adequate -ventiation. -After the -stain has been I"emoved, it is good practice to wash the area copiousy with cear water to remove any residua contamination and to be certain that no soube and possiby detrimenta sats remain on the concrete. 2

19 PART III: EVALUATION OF STAIN REMOVAL METHODS USING MORTAR SPECIMENS 28. In order to evauate the most promising methods of remova of the most common stains found on concrete as reveaed by the iterature search, mortar specimens were prepared and stained with iron, ubricating ois, and asphat. These stains were then removed by appropriate methods. Detais of the tests conducted are outined in the foowing paragraphs. Iron Stains Preparation of mortar specimens 29. Seventy-two mortar specimens were prepared in three rounds consisting of four batches per round. The specimens were prepared with type II portand cement and graded Ottawa sand and were proportioned and mixed in accordance with Method CRD-C , section 5(a) and 5(b)(2).7 Six specimens, 6 by 6 by 3/4 in., were moded from each batch as outined in Method CRD-C 26-63, section 5(e).7 Immediatey after moding, the specimens were paced in the fog room, which was maintained at 73 F and 00 percent reative humidity. The specimens were removed from the mods 48 hr after moding, and three specimens from each batch were coated on the test surface with a cear conr...rete curing_ compound_ in_ ac_coxd.ance_ wlth Method CRD-C , section 5(g).7 The coated specimens were stored at 73 F in aboratory air, and the three remaining specimens from each batch were returned to the fog room for an additiona 24 hr. Appication of stain 30. When the specimens attained an age of 72 hr, they were paced under infrared amps, and a soution of ferric choride was added in sma increments to the test surface and evaporated unti stain was considered to be either mid or severe. Haf of the test specimens were stained to a mid condition, requiring 350 m of a 00-ppm FeC3 soution, and the remaining haf were stained to a severe condition, requiring 600 m of the 00-ppm Fec soution. The precoated specimens received the same quantity 3 of staining soution as appied to the pain specimens for each stain 3

20 condition. The stain conditions were deveoped in ess than 6 hr, and the temperature of the specimens was not aowed to reach more than 40 F during the staining process. A stained specimens were stored in the aboratory at 73 F for a minimum of 28 days before remova methods were tested and evauated. Remova methods 3. Four chemica remova procedures and three mechanica procedures were evauated on mortar specimens representing either mid, severe, or both stain conditions. Two specimens were avaiabe for each combination of stain condition and remova method for each of the three rounds. As indicated above, one specimen was coated with curing compound prior to being stained, and the other received no specia treatment. The combinations of stain conditions and remova methods were as foows: Stain Condi ti on (Fec 3 ) Mid Mid Mid Severe Severe Severe Mid Mid Mid Severe Severe Severe Remova Method Oxaic acid wash Sodium citrate, gycerin, Caco 3 poutice Ammonium citrate, gycerin, Caco 3 ~outice sodium citrate, gycerin, CaC03 poutice Ammonium citrate, gycerin, CaC03 poutice Sodium citrate, sodium hydrosufite, CaC03 poutice Sandbast Water jet Water surry jet Sandbast Water jet Water surry jet 32. The chemica methods of iron stain remova used foowed the procedures outined in Part II exacty, but the mechanica methods were atered as foows to make them appicabe to the sma mortar specimens. a. Sandbast. The stained mortar specimens were moved in a horizonta path under the sand-air stream of a sma 4

21 stationary sandbast machine, and sufficient passes were made to expose the entire stained area to the stream. b. Water Jet. The stained faces of the mortar specimens were hed at an ange of 45 deg, and the water-jet stream was projected in a horizonta path across the surface. The path was directed so that the upper portron of the face received the water jet first, and successive passes progressed down the face unti the entire surface had been exposed. operating air pressure was 90 to 95 psi over the water in the tank. c. Water surry Jet. The test specimens were subjected to the water surry jet in the same manner that they were subjected The to the water jet. The surry was composed of 20 b of fy ash per 5 ga of water and had been stirred we before appication of air pressure. Discussion of resuts 33. The stain remova methods were evauated by visua inspection, and a numerica rating seected from the foowing ist was assigned to each specimen. Evauation Compete remova Amost compete remova Partia remova Light or poor remova No remova or ineffective Numerica Ratin~ Resuts of the iron stain remova tests are shown in the tabuation on the foowing page. 34. The minimum tota score that can be obtained by any one remova method for one condition is 3, and the maximum tota is 5. A score of 3 indicates that the stain remova method is very effective, whereas a score of 5 indicates that the method is competey ineffective. An examination of the tabuation reveas that the effectiveness of the iron stain remova methods may be categorized as tending to have either a rating of, compete remova, or a rating of 4 to 5, poor to no remova. 5

22 Effectiveness of Various Remova Methods in Ceaning Iron-Stained Mortar Specimens Mid Stain Severe Stain Curing- Curing- Compound- Compound- Pain Coated Pain Coated Round Round Round Round Remova Method 2 2 _3 2_]. 2 _3_ Oxaic acid Tota (3) 2* 4* (0) 4* Na citrate, gycerin, CaC03 Tota * () 4* (2) 4* * () 4* (2) 4* NH4 citrate, gycerin, CaC03 Tota * () 3* () 4* * () 3* () 4* Na citrate, Na hydrosufite Tota 2 5* ( 4) 4* (3) 4* Sandbast Tota (3) (3) -Water j-et ** 4** 4** 5 Tota (5) (2) Water surry jet Tota * 5 5 (5) 5 4** 5 (4) ( 3) 5 (5) (5) ( 3) 5 4** 4** 4** (2) 5 4** 5 (4) Stain was embedded in membrane, but rinsing and scraping removed the stained membrane, eaving a cean mortar surface. ** Stain was embedded in membrane, but proonged exposure to water jet did oosen membrane somewhat, permitting sight remova of stain Methods of removing iron stain from mortar are apparenty not dependent upon the severity of the stains at the concentrations used in this investigation, since the effectiveness of the remova methods was found to be the same for both mid and severe stains. 36. One of the reasons for coating the specimen with curing compound was to prevent the stain from penetrating the mortar. However, it 6

23 was found that the stain penetrated the coating, necessitating compete remova of the membrane to remove the stain. 37. The resuts show that the most effective means of those evauated for removing iron stains from both pain and curing-compound-coated mortar specimens is sandbasting, which competey removed the stain from the specimens. The precoated specimens were somewhat easier to cean by mid sandbasting, which resuted in ess abrasion at the surface than it did on the pain mortar specimens. 38. The oxaic acid remova technique was equa in effectiveness to sandbasting for the pain mortar, but was not very effective in removing stains from precoated mortar. 39, Stain remova using the sodium citrate-sodium hydrosufite mixture was amost as effective as sandbasting for pain mortar, but not very effective for precoated specimens. The water and water surry jets were competey ineffective in removing stains. The sodium and ammonium citrate methods aso resuted in poor remova of the stain. However, a second appication of the citrate poutices woud undoubtedy have removed additiona stain and woud be desirabe if these methods are used for remova. 40. Proonged treatment with water and water surry jets of the surfaces of the precoated specimens oosened the membrane and aowed some stain remova aong with the membrane, whereas no stain remova was produced on the pain mortar. Difficuty was experienced in the operating equipment for the water surry jet. The fy ash used in the surry setted too quicky and aso stopped up the nozze of the hose. However, additiona pressure and increased agitation to keep the fy ash in suspension might increase the effectiveness of the method. Lubricating Oi and Asphat Stains Specimen preparation 4. Twenty-four mortar specimens.were prepared in two rounds consisting of two batches per round. The specimens were prepared in the same manner as those used in the iron stain tests except that none of the 7

24 specimens were coated with curing compound, and a specimens remained in the fog room for 7 days. After 7 days, the specimens were moved to the aboratory and stored there at 73 F for an additiona 7 days. Tweve of the specimens were then coated on the test surface with a uniform coating of used ubricating oi, and tweve were coated with cutback asphat. Both the oi and asphat were appied to the mortar surfaces at the rate of 300 sq ft/ga with a sma paint brush. The specimens were then stored in the aboratory for an additiona 4 days prior to the testing of the remova methods. Methods of removing ubricating oi stains and resuts 42. The remova methods used for ubricating oi were (a) Na3P04- Caco3 mixture, (b) 5 percent NaOH-CaC03 mixture, and (c) benzene-caco 3 paste. Methods of mixing pastes and appications are described in paragraph 4!'!:_-.. of the methods. Compete remova of the oi stains was not attained by any either the Na 3 Po4 or NaOH methods. The benzene-cac03 paste remova method was superior to The second best method was appication of the 5 percent NaOH-CaC03 poutice. A repeat appication of this mixture on two of the specimens resuted in ony sight improvement of stain remova. Because itte _oi was removed from mortar specimens using the Na 3 P04-Caco 3 mixture, the method is considered competey unsatisfactory. A second appication of the Na3P04-CaC03 paste on the stained surface caused itte or no improvement in the remova of the oi stain. Methods of removing asphat stains and resuts 43. The excess asphat was scraped off with a putty knife on a the asphat-stained specimens. Six of the specimens were treated with benzene Caco3 paste, which was aowed to remain on the stain for 3 hr, foowed by scrubbing with soap powder, water, and a stiff brush. The asphat stain was not competey removed by this method, but it is beieved that additiona treatments might have resuted in more compete stain remova. six remaining asphat-stained mortar specimens were treated with a soution made of equa parts of dimethy sufoxide and water, and the surfaces The 8

25 were then scrubbed with this soution and a stiff brush. No remova of stain by use of this method was detected. 9

26 PART IV: EVALUATION OF STAIN REMOVAL METHODS ON CONCRETE SPECIMENS 44. The second phase of this investigation indicated that the foowing chemica and mechanica methods for removing stains were the most effective: (a) oxaic acid, sodium hydrosufite, and sandbasting for iron stains; and (b) benzene-caco 3 mixture and sandbasting for ubricating oi and cutback asphat stains. Therefore, these methods were evauated using formed concrete surfaces. The water jet procedure was atered and evauated for remova of iron stains; the ateration consisted of scrubbing the specimens with a wire brush, water, and soap powder. Preparation of Concrete Specimens 45. Tweve concrete specimens, 4 ft by 4 ft by 3 in., were prepared in three rounds consisting of four specimens per round; ony one batch of concrete was mixed for each round. The specimens were prepared with type II portand ce~ent, 3/4-in.. maximum size imestone aggregate, imestone sand, and air-entraining admixtures, mixed and processed in accordance with -Method --crd--c -ro..;t)i. 7 T"he mxture had a sump of' 2-/2 in. and an unconfined compressive strength of 3000 psi at 28 days age. Immediatey after moding, the specimens were paced in the fog room, which was maintained at 73 F and 00 percent reative humidity. Specimens were removed from the mods 48 hr after moding. Two specimens from round and three specimens each from rounds 2 and 3 were stored in the fog room unti needed for staining. The remaining four specimens were coated on the test surface (formed surface) with cear concrete curing compound, in accordance with CRD-C The coated specimens were stored at approximatey 73 Fin aboratory air. The pain specimens were removed from the fog room after 28 days. Iron Stain Appication of stain 46. Eight of the 2 specimens were used to evauate the effectiveness 20

27 of iron stain remova methods. Four of these eight specimens were coated with cear curing compound. The four specimens of round (2 pain and 2 with curing compound), three specimens from round 2 (2 pain and with curing compound), and one specimen with curing compound from round 3 were paced in a constant-temperature room (20.:t, 5 F) and stained. A soution of ferric choride was appied in -/2-ga increments to the test surfaces and aowed to evaporate unti a severe staining condition was obtained; this required approximatey 2400 m of 00-ppm Fec 3 soution for each ~sq :f't area. Pre coated and pain specimens received the same quantity of staining soution. Severe staining (deep reddish-brown coor covering about 95 percent of test surface) was obtained in approximatey seven working days. The eight iron-stained specimens were then stored at 73 F for a minimum of 28 days before testing of remova methods was started. Remova methods 47. Two remova methods were evauated for each of the eight specimens (four pain and four curing-compound-coated). One mechanica remova method was used on haf of each iron-stained surface, whereas a chemica method was used on the remaining haf. The foowing tabuation shows the severe iron stain remova methods used, the surface condition, and mixture and specimen number. occasions. Re-peat remova operations were- empoyed on severa Remova Methods Used on Pain Surface SEecimens Coated Surface SEecimens R-- R--2 R-2- R-2-2 R--3 R--!i R-2-3 R-2-!i Oxaic Wire brush Oxaic acid Sand- Oxaic acid Sand- Oxaic Wire brush acid and water basting basting acid and water jet jet Sand- Hydro- Wire brush Hydro- Wire brush Hydro- Sand- Hydrobasting sufite and water sufite and water sufite basting sufite jet jet Note: A -in.-wide stained strip was eft on the specimens for comparative purposes. 48. Sandbasting was accompished with a sma portabe aboratory rig. The portion of a basic siica sand passing the No. 30 and retained on the No. 50 sieve was subjected to 60 b of compressed air and forced through a /4-in.-diam nozze onto the test surface. The nozze was hed at a 45-deg ange to and 0 in. from the test surface. 2

28 Discussion of resuts 49. The effectiveness of each remova method was evauated by one or a combination of the foowing methods: (a) thoroughness of stain remova, (b) time and effort invoved in removing stain, (c) effect on concrete surface, and (d) cost based on -sq-ft area. The thoroughness of stain remova was evauated by the visua inspection method described in paragraph 33, The remaining three evauation methods are described beow. a. Time and effort invoved in removing stain. () the actua time required for preparation, appication, and remova of a stain remova agent(s), or the time an agent was on the test surface (waiting time was not taken into account); and (2) the nature of the effort expended, which is described herein as either easy or hard. b. Deeterious effects on the concrete surface. The apparent deeterious effects were discooration and oss of mortar materia. c. Materia costs of sma quantities ( to 5 b). Costs of technica grade chemicas and manufactured grade sand (50-b bag) were used in computing the materias cost per square _f'nnl ~or each stain remova method. Buk purchases of materias, different pay scaes, high-production sandbasting equipment, etc., woud greaty infuence the overa cost of a particuar job. Aso, the cost of water woud vary from area to area; therefore, the quantity of water used is noted instead of water cost. 50. The costs of materias used are shown in the foowing tabuation: Materia Costs and Quantities Used per Square Foot of Concrete Surface Materia guantit~ Cost* Sodium citrate b $0.44 per b Sodium hydrosufite b $0.20 per Th Oxaic acid.000 b $0.324 per Th Benzene 0.25 ga $2.850 per ga Cacium carbonate powder b $0.24 per b Sand, -30 to +50 4Tu $0.027 per Tu * These costs are based on price ists in effect in 967 for sma quantities of chemicas. 22

29 5. The effectiveness, denoted by ranks as outined in paragraph 33, of the four different remova methods is shown in the foowing tabuation. The time and effort, observed effects, and costs are aso given. With ony two exceptions, identica resuts were obtained for both the pain and the curing-compound-coated specimens. Therefore, no differentiation is made in the tabuation between these two specimen types except to note where the resuts differed. In addition, simiar resuts were obtained for each of the two repicates tested for each method. Method Oxaic acid Hydrosufi te Sandbasting Wire brush and water jet Effectiveness of Various Methods in Removing Iron Stains from Concrete Surfaces Time Materia Expended Nature Cost Per Visua man-hr/ of Square Rank sg ft Effort Observed Effects Foot* 2** t Hard Easy Easy Hard Incompete iron stain remova Non et Removed /6-in. ayer of matrix Incompete iron stain remova, a:nd removed /32-in. ayer of matrix $0.324 $0.028 $0.08 $0.000 Quantity of Water Used 2 ga tt * Materia costs do not incude cost of water or equipment. ** Ranking shown is the resut of a second appication; ranking after first appication was 3. t Ony a sight yeow tinge was evident on curing-compound-coated specimens; for these specimens, the visua rank was 2. tt Ony 30 ga of water was used on curing-compound-coated specimens. 52. The resuts obtained on concrete surfaces and aso on mortar surfaces indicate that a coating of curing compound does not prevent iron stain nor does it make the task of stain remova any easier. The additiona cost of appying curing compound to concrete surfaces is not warranted if water curing is to be used. 53. The resuts aso indicate that the most effective methods of 23

30 removing iron stain are sandbasting and appication of hydrosufite. The ony adverse effect of sandbasting is the remova of mortar materia. The soidum citrate~sodium hydrosufite remova method is equay as effective as sandbasting, has no adverse effect on the uncoated concrete surface, and is the east expensive of the procedures evauated. The oxaic acid remova technique was next in effectiveness, but it did not competey remove the iron discooration on the pain specimens. The east effective method was the wire brush and water jet technique. 54. The wire brush and water jet technique did not competey remove the iron discooration, and some of the mortar was removed. This technique aso required more man-hours per square foot and consideraby more water than any of the other remova methods investigated. However, in some cases where iron stains are not very severe and occur in sma but numerous areas, this method may be more appicabe than the chemica methods. Appication of stains Lubricating Oi and Asphat Stains 55, The four specimens were prepared as described in paragraph 45. A~er the specimens had cured for 28 days in the fog room, they were stored in aboratory air at 73 F and then stained. Two specimens each were uniformy coated with used ubricating oi and cutback asphat at a rate of 300 sq -rt/ ga with a 4-.;n. -Urush. Remova inethods -were started when the specimens attained an age of 56 days. Remova methods 56. Three remova methods were used on each of the four stained surfaces (two oi and two asphat). The three remova methods used were (a) benzene-caco 3 paste, (b) sandbasting, and (c) wire brush. Methods of mixing the benzene-caco 3 paste are described in paragraph 4_. The sandbasting was conducted as outined in paragraph 48, and the wire brush technique invoved scrubbing the concrete surfaces with a wire brush, soap powder, and tap water. Discussion of resuts 57. The effectiveness, the time and effort, observed effects, manhours expended, and costs of materias are given in the foowing tabuation: 24

31 Effectiveness of Various Methods in Removing Lubricating Oi and AsEhat Stains from Concrete Surfaces Quantity Time Materia of Expended Nature Cost Per Water Visua man-hr/ of Square Used Method Rank sg ft Effort Observed Effects Foot ga Lubricatins Ois Benzene-Caco 3 * Hard None $ Sandbasting Easy Removed /6-in. $0.08 ayer of matrix Wire brush Hard Oi $ discooration AsEhat Stains Benzene-CaC03 2** Hard Asphat $ /2 discooration Sandbasting Easy Sat and pepper $0.08 appearance Wire brush 3t Hard Incompete $ * Ranking shows the resuts of third appication; second appication was 2, and first appication was 3. ** Ranking shows the resut of third appication; second appication was 3, and first appication was 4. t Ranking shows resut 0--- second appication; rrrst appiication was Compete remova of the oi stains was attained by the benzene Caco3 paste and the sandbasting methods. However, it was necessary to appy the benzene-cac03 mixture three times before compete remova was achieved. effective. The wire brush and running water remova method was the east 59, Excess asphat was scraped off the asphat-stained specimens before remova methods were started. The benzene-caco 3 paste was aowed to remain on the stain for 3 hr. The test surface was then scrubbed with soap powder, water, and a wire brush. to remove the asphat stain competey. Three such appications faied The benzene-cac03 paste probaby caused penetration of the stain and made compete remova impossibe. 25

32 60. The sandbasting technique amost competey removed the stain, but as in the case of the iron-stained specimens, the forced sand removed some matrix. The asphat was quite fuid when appied to the concrete specimens, and migrated into numerous sma surface voids. Most of the asphat contained in these voids remained after sandbasting and gave the test surface a sat and pepper appearance. 6. The east effective remova method was the wire brush, soap powder, and running water. Three appications faied to remove the asphat satisfactoriy; a thin fim of asphat remained on both specimens. From the tabuation in paragraph 57, it can be seen that this remova technique required by far the most man-hours per square foot. By comparing abor and materias costs per square foot, it is evident that ubricating oi and asphat stains are far more expensive to remove than are iron stains. For exampe, it requires about 36 times as many man-hours per square foot to partiay remove asphat stains by wire brushing than to remove iron stains by sandbasting. If the sandbasting techniques for iron and asphat stain remova are compared, it can be seen that the asphat stains sti require approximatey three times as much time to remove as the iron stains. 26