1、BRITISH STANDARD BS 4550-3.8: 1978 Methods of testing cement Part 3: Physical tests Section 3.8 Test for heat of hydration IMPORTANT NOTE. It is recommended that this Section be read in conjunction with the information in the “General Introduction” to BS4550 and with the information in BS4550-3.1, w
2、hich are both issued separately. UDC 666.94.01:620.1:536.664BS4550-3.8:1978 This British Standard, having been prepared under the directionof the Cement, Gypsum,Aggregates and QuarryProducts Standards Committee, was published underthe authority of the Executive Board on 30June1978 BSI 03-1999 The fo
3、llowing BSI references relate to the work on this standard: Committee reference CAB/1 Draft for comment 73/10751 DC ISBN 0 580 10143 6 A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application.
4、Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 10, an inside back cover and a back cover. This standard has been updated (see copyright date) and m
5、ay have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date of issue CommentsBS4550-3.8:1978 BSI 03-1999 i Contents Page 1 Test principle 1 2 References 1 3 Materials 1 4 Apparatus 1 5 Determination o
6、f heat capacity 2 6 Calculation of heat capacity and thermal leakage coefficient 2 7 Preparation of hydrated cement samples 3 8 Determination of heat of solution 3 9 Determination of water content 3 10 Calculations 4 Figure 1 Typical calorimeter 8 Figure 2 Apparatus for determining water content 9 P
7、ublications referred to Inside back coverii blankBS4550-3.8:1978 BSI 03-1999 1 1 Test principle The heat of hydration of cement is determined calorimetrically based on the difference in the heat of solution between the unhydrated and the hydrated cement. It is expressed in kilojoules per kilogram an
8、hydrous mass. The method when applied to cements other than Portland cements requires the determination of water content. For Portland cements the procedure may be simplified by replacing this determination by that for loss-on-ignition in accordance with clause13 of BS4550-2:1970. 2 References The t
9、itles of the publications referred to are listed on the inside back cover. 3 Materials 3.1 For the determination of heat of solution, make up in bulk2.00+0.05M nitric acid from analytical reagent quality materials and a40% m/m solution of analytical reagent quality hydrofluoric acid. NOTEBulk prepar
10、ation of the mixture of these acids in the required porportions is permissible and the bulk mixture should be stored in a non-reactive container. 3.2 For the determination of heat capacity, use analytical reagent quality zinc oxide. 3.3 For the determination of water content, use dried magnesium per
11、chlorate containing not more than14% of moisture. WARNING NOTE. Hydrofluoric acid can produce painful skin burns that heal only with difficulty and precautions in handling this very corrosive substance should be observed. Attention is also drawn to the handling of magnesium perchlorate which is a po
12、werful oxidizing agent and should not be brought into contact with substances that could cause possible ignition or explosion. 4 Apparatus The following apparatus is required. 4.1 Calorimeter. The calorimeter shall consist of a150mm 75mm diameter open mouthed vacuum flask with a cork or rubber stopp
13、er40mm thick; an insulated container for the flask; a thermometer (range6C with an accuracy of 0.001C) with reading lens, or any other temperature measuring device which gives the same degree of accuracy; a constant speed stirrer; and a funnel for the introduction of the sample. A typical calorimete
14、r is shown inFigure 1. The flask shall be of such a kind that: a) when filled with398ml of water, the water surface is20 5mm below the lower surface of the stopper; b) when the flask is filled with400ml of warm water, the temperature loss, determined after standing without stirring for approximately
15、30min, does not exceed0.002C/min perC above room temperature. The whole inner surface of the vacuum flask, the underside of the stopper and the parts of the thermometer and the stirrer, if made of glass, which protrude beneath the stopper, shall be evenly and thinly covered with a suitable acid-proo
16、f coating. NOTEA suitably adherent coating may be prepared by melting together equal parts by mass of paraffin wax and petroleum jelly. Alternatively, strip-off lacquer has been found suitable. To resist damage through wear and tear the mouth of the vacuum flask is given an additional coating of pur
17、e paraffin wax. Should the coating at any time become damaged, as revealed by visual examination, or by anomalous increases in temperature, remove the whole coating and renew it. The container shall have an insulating layer of cork, cotton wool or similar material at least25mm thick, completely encl
18、osing the flask, and also providing support for the flask and the stirrer motor. It is important that the insulation be kept dry and intact since the heat capacity of the apparatus is seriously affected by changes of this sort. The container is divided in a vertical plane into two halves, which are
19、hinged together at one side and provided with a fastening device at the other. The thermometer shall be adjusted so that the upper end of the range approximates to25C and its zero is recorded by reference to another thermometer to 0.1C. It shall be rigidly held by the stopper so as to avoid accident
20、al contact with the stirrer blades. In order to facilitate removal of the thermometer, the stopper may be divided into two halves, one of which supports the thermometer and the other the funnel.BS4550-3.8:1978 2 BSI 03-1999 The stirrer, which shall be of the double-bladed propeller type, approximate
21、ly40mm in diameter, is made from plastics or glass, and extends to within40mm of the bottom of the flask. The pitch of the blades shall be set in such a manner that, when the stirrer is actuated by the drive motor, liquid in the flask is propelled in a downward direction. Means are provided for disc
22、onnecting the stirrer from the motor, which shall be synchronous motor geared to run at a constant speed of approximately400r/min. The heat developed by the stirrer when running continuously shall be such that the contents of the flask will not rise in temperature at a rate greater than0.001C per mi
23、nute over and above the rate of temperature change in the unstirred condition. The funnel is of the Gooch type with a stem of6mm internal diameter and a body approximately25mm long and25mm in diameter. The stem shall not protrude more than 3mm beneath the cork stopper. During the course of the deter
24、mination take every precaution to maintain steady room temperature conditions, e.g.by avoiding draughts or direct sunshine. It is desirable that the room temperature variation should not exceed 0.5 C. 4.2 Water content determination apparatus. The apparatus shall consist of a small vessel containing
25、 “dried” magnesium perchlorate, through which a stream of air or nitrogen is passed before entering a silica combustion tube that is heated in a furnace capable of reaching1000C (bright red heat). The exit from the combustion tube shall be packed with silver wool. NOTEIf silicone rubber connections
26、are used it is advisable to protect them with heat reflectors. The gas leaving the combustion tube shall be passed through two weighable absorption tubes. The first quarter of each absorption tube is packed with silica gel and the remainder with “dried” magnesium perchlorate. A bubbler containing su
27、lphuric acid is fitted after the exit end of the second absorption tube to allow the gas flow to be observed. (Figure 2 shows one method of achieving these requirements.) 4.3 Balance with case. The balance shall be capable of weighing up to at least10g, to an accuracy of 0.001g. 4.4 Test sieves. Two
28、 test sieves of nominal aperture2124m and8504m respectively, complying with the requirements of BS410. 4.5 Desiccator containing anhydrous calcium chloride. 5 Determination of heat capacity Determine the heat capacity whenever a new batch of nitric acid is prepared, or any modification, however mino
29、r, is made to the apparatus used. Ignite for1h at900C to950C enough zinc oxide for about six determinations, cool in the desiccator and grind to pass a2124m test sieve. For each determination, again heat to900C to950C for5min about7.0g of this ignited oxide and then cool for not less than2.5h and no
30、t more than5h in the desiccator, before weighing to 0.001g. Inspect the vacuum flask coating for faults and then measure into the calorimeter414.0 0.1g of the nitric acid and10.8 0.1g of the hydrofluoric acid. Assemble the calorimeter and run the stirrer for at least10min to attain thermal equilibri
31、um. Then record the temperature ( 0 ) to 0.001C, and again after10min( 10 ). Towards the end of this10min period record the temperature of the zinc oxide to the nearest0.1C. Immediately after the 10min reading introduce the zinc oxide through the funnel steadily over a period of not less than1min an
32、d not more than2min; brush into the calorimeter by means of a camel hair brush any material adhering to the funnel, and material adhering to the brush should be tapped off into the calorimeter. Record the temperature at30min ( 30 ) and40min ( 40 ). 6 Calculation of heat capacity and thermal leakage
33、coefficient 6.1 The uncorrected temperature rise is the difference between the 10min and30min readings,( 30 10 ). The correction to be added is twice the fall in temperature between the 30min and 40min readings, ( 30 40 ). Corrected temperature rise (C) = ( 30 10 ) + 2( 30 40 ) (1)BS4550-3.8:1978 BS
34、I 03-1999 3 6.2 Calculate the heat capacity as follows: Heat capacity (J/C) where This expression simplifies to: 6.3 Calculate the thermal leakage coefficient K as follows: 7 Preparation of hydrated cement samples Mix by stirring for 4min in a suitable container one part by mass of the cement and0.4
35、parts by mass of distilled water at a temperature of15C to25C and use this paste to fill a glass specimen tube(50mm 25mm diameter nominal size) to provide a sample for test at each required age. Quantities of60.0g of cement and24.0g of distilled water are adequate for two samples. Cover the exposed
36、surface of the filled specimen tube with a layer of molten paraffin wax, insert a cork and seal with a further coating of paraffin wax. Store the specimen tube in a vertical position at20 1C until the time of test. NOTEOccasionally, trouble may be experienced with bursting of glass specimen tubes ar
37、ising from slight expansion of the setting cement paste. In the event of such difficulty, use sealed polythene vials, of adequate thickness to resist transmission of water vapour, in place of glass tubes. 8 Determination of heat of solution 8.1 Unhydrated cement. Place the sample of unhydrated cemen
38、t in an airtight bottle and make heat of solution determinations on three separate sub-samples of about3.0g each within seven days of preparing the hydrated sub-samples (clause7). Weigh each sub-sample to 0.001g. Make the determination of the temperature rise exactly as described for zinc oxide (cla
39、use5), except that the reading of 40is omitted. 8.2 Hydrated cement. Break open the appropriate specimen tube at the required age, and remove all adherent wax and glass from the hydrated cement sample. Then grind the sample (as rapidly as possible to avoid carbonation) to pass a8504m test sieve. Pla
40、ce the ground sample in an airtight bottle and make heat of solution determinations on three separate sub-samples of about4.2g each. Weigh each sub-sample to 0.001g. Make the determination of the temperature rise as for the unhydrated cement. 9 Determination of water content NOTEThis determination i
41、s not required for Portland cements (seeclause1). Make water content determinations on two separate sub-samples of about2.0g each for unhydrated cement and about1.0g each for hydrated cement, at the same time as the corresponding heat of solution determinations. 1076.9 is the heat of solution of zin
42、c oxide at30C (in J/g) 0.36 is the negative temperature coefficient of the heat of solution t is the final temperature of the calorimeter and contents (in C) (= 30+ thermometer zero) 0.50 is the specific heat of zinc oxide T is the temperature (inC) of the zinc oxide at the time of introduction into
43、 the calorimeter Heat capacity (J/C) (2) K (C/10 min perC change in temperature) (3)BS4550-3.8:1978 4 BSI 03-1999 Purge the apparatus of residual moisture by removing the absorption tubes and passing dried gas through the combustion tube, heated to1000C. After15min replace the absorption tubes and c
44、ontinue heating for another15min. Remove the source of heat and continue the gas flow for a further15min. Again remove the absorption tubes from the apparatus and transfer to the balance case. When the combustion tube has cooled to below100 C, weigh the absorption tubes to 0.001g and fit into the tr
45、ain. Weigh to 0.001g approximately2.0g of unhydrated cement or approximately1.0g of hydrated cement into a combustion boat previously ignited to constant mass at1000C and promptly insert into the combustion tube from the inlet end. Replace the connection and adjust the rate of gas flow to about thre
46、e bubbles per second at the bubbler. Heat, cautiously at first, to a temperature of1000C and maintain for30min. Drive any water condensed in the end of the combustion tube into the absorption tube by slight external warming of the combustion tube, care being taken not to heat the absorption tube. Re
47、move the source of heat and continue to pass air for a further15min. Disconnect the absorption tubes, transfer to the balance case and weigh after15min. Make a blank determination preferably on the same day, using an empty boat but in other respects following the procedure previously described. If t
48、he gain in mass of the absorption tube during the blank determination exceeds0.003g, the apparatus shall be checked and the determination repeated. Subtract the gain in mass during the blank determination from the gain in mass during the water content determination and express as a percentage of the
49、 original mass of the sample. Take the average of two determinations of water content and express the result to the nearest0.1%. NOTEThe method described is based on the normal procedure for the gravimetric determination of water. With hydrated cement samples which have a high water vapour pressure it is important that, when the sample is placed in the tube, collection of water should be commenced immediately. The normal practice of flushing out the apparatus with dry air when the sample is first placed
