APPENDIX C-Continued 



APPENDIX 4— 



HEAVYWEIGHT CONCRETE MIX 



PROPORTIONING 



A4.1 — Concrete of normal placeability can be propor- 

 tioned for densities as high as 350 lb per cu ft by using 

 heavy aggregates such as iron ore, barite, or iron shot 

 and iron punchings. Although each of the materials has 

 its own special characteristics, it can be processed to 

 meet the standard requirements for grading, soundness, 

 cleanliness, etc. The acceptability of the aggregate 

 should be made depending upon its intended use. In 

 the case of radiation shielding, determination should be 

 made of trace elements within the material which may 

 become reactive when subjected to radiation. In the 

 selection of materials and proportioning of heavyweight 

 i.oncrete, the data needed and procedures used are 

 similar to that required for normal weight concrete 

 except that the following items should be considered. 



A4.1.1 — In selecting an aggregate for a specified 

 density, the specific gravity of the fine aggregate should 

 be comparable to that of the coarse aggregate in order 

 to lessen settlement of the coarse aggregate through the 

 mortar matrix. Typical materials used as heavy aggre- 

 gates include the following: 



Material 



Description 



Speclfic 

 gravity 



Approx. 

 unitwt 1 



Ib/cuft) 



IJmonlte 

 Goethite 



Hydrous Iron 



3-4 - 3.8 



180 



-195 



Barite 



Barium sulfate 



4,0-4.4 



205 



-225 



Ilmenite 

 Hematite 

 MagneUt« 



.rono.es 



4.2-4.8 



215 



-240 



Iron 



Shot, pellets. 

 punciLings. etc- 



65-7.5 



310 



-350 



Ai.l2 — When the concrete in service is to be ex- 

 posed to a hot, dry environment, it should be propor- 

 tioned so that the fresh urTit weight is at least 10 lb 

 per cu ft higher than the required dry unit weight. 



A4.1.3 — When entrained air is required to resist con- 

 ditions of exposure, allowance must be made for the 

 loss in weight due to the space occupied by the air. 

 To achieve adequate consolidation using high frequency 

 vibrators and close insertion intervals, without the 

 excessive loss of entrained air, plastic concrete should 

 be designed for a high air content to offset this loss 

 during placement. 



A4.1.4 — Heav>'^'eight concrete is often used for radi- 

 ation shielding. In this case, the aggregate type and 

 concrete weight should be selected consistent with the 

 type of radiation involved. Generally speaking the 

 greater the mass the belter are the shielding properties 

 against gamma and beta rays. However, neutron at- 

 tenuation depends more on the specific elements present 

 in the concrete, i.e., hydrogen, carbon, boron, etc. 



A4.1.5 — Ferrophosphorous and ferrosilicon (heavy- 

 weight slags) materials should be used only after 

 thorough scrutiny. Hydrogen evolution in heavyweight 

 concrete containing these aggregates has been known to 

 result in a reaction of a self-limiting nature, producing 

 over 25 times its volume of hydrogen before the reac- 

 tion ceases. 



A4.1.6— In Section 5 3.7 (Step 7) caution must be 

 exercised if the weight method (Section 5.3.7.1) is used 

 to estimate the fine aggregate batch weight. The values 

 in Table 5.3.7.1 must be corrected for overall aggregate 

 specific gravity since the table is based on an average 

 aggregate specific gravity of 2.7. Therefore, it is recom- 



mended that the required amount of fine aggregate be 

 determined by the absolute volume procedure (Section 

 5.3.7.2). 



A4.2 — Prodiiction and quality control. The technique 

 and equipment for producing heavyweight concrete 

 are the same as used with normal weight concrete. In 

 the selection of heavyweight materials and combina- 

 tions thereof for the purposes of proportioning speci- 

 fication concretes, attention must be directed to 

 aggregate effects on placeability, strength, and dura- 

 bility of the concrete. Testing and quality control 

 measures assume greater importance than with normal 

 weight concrete. Control of aggregate grading is essen- 

 tial because of the effect on the placing and consolidat- 

 ing properties of concrete, and on the unit weight of 

 the concrete. In enforcing strict quality control special 

 attention should be paid to the following: 



A4.2.1 — Prevention of contamination with normal 

 weight aggregate in stockpiles and conveying equip- 

 ment. 



A4.2^ — Purging of all aggregate handling and batch- 

 ing equipment, premixers and truck mixers, before 

 batching and mixing heavyweight concrete.- 



A4.2.3 — Accuracy and condition of conveying and 

 scale equipment, aggregate storage and concrete batch- 

 ing bins. Due to the greater weight of heavyweight 

 aggregate, the permissible volume batched in a bin is 

 considerably less than the design capacity. For ex- 

 ample: a 100 ton aggregate bin designed for 75 cu yd 

 of normal weight aggregate should not be loaded with 

 more than 25 to 55 cu yd for the range of specific 

 gravities shown in Section A4.1.1. 



A4.2.4 — Condition and loading of mixing equipment 

 For concrete of a weight range of approximately 4800 

 to 9500 lb per cu yd, the capacity of a truck mixer, 

 without overloading, is reduced from 20 to 60 percent. 



A4.2.5 — Accurate aggregate proportioning to main- 

 lain w/c ratio. Degradation of some coarse heavy- 

 weight aggregates, iron ores in particular, is another 

 production problem which should be carefully con- 

 trolled. Either the coarse aggregate should be rescreened 

 immediately prior to incorporation into the concrete 

 or adjustments made in the mixture proportions that 

 compensate for the increased percentage of fines in the 

 coarse aggregate, caused by aggregate breakdown dur- 

 ing handling. Therefore, caution should be exercised 

 and frequent gradation checks made on stockpiled 

 aggregates. 



A4.2.6 — Frequent checks of fresh unit weight. 



A4.2.7 — Design ^nd construction of forms to handle 

 additional weight of concrete. 



A4.2.8 — Vibrators for consolidation. 

 A4J — Example problem. Concrete is required for 

 counterweights on a lift bridge not subjected to freezing 

 and thawing conditions. An average 28-day compressive 

 strength of 4500 psi will be required. Placement con- 

 ditions permit a slump of 2 to 3 in. and a maximum size 

 aggregate of 1 in. The design of the counterweight re- 

 quires a dry unit weight of 230 lb per cu ft. An in- 

 vestigation of economically available materials has 

 indicated the following: 



Cement —Type I (non-alr-entralnlng) 



Fine aggregate —Specular Hematite 



Coarse aggregate —Ilmenite 



The table in Section 4.1.1 indicates that this combina- 

 tion of materials may result in a dry unit weight of 215 

 to 240 lb per cu ft. The following properties of the 

 aggregates have been obtained from laboratory tests: 



ACI STANDARD 



337 



