Compums Edur. Vol. 13, No. 1, pp. 6946, 1989 0360-1315189 S3.Mlt0.00 Printed in Great Bdtatn. All rights reserved Copyright ,c 1989 Pcrgamon Press pk

AN EXPERT SYSTEM FOR TEACHING CONCRETE MIX DESIGN

SIRIPONG MALASRI* and SANTIAC~ MALDONADO

Department of Civil and Architectural Engineering, University of Miami, Coral Gables, FL 33124, U.S.A.

(Receired 4 January 1988; in recked form 24 June 1988)

Abstract-An expert system has been developed for teaching concrete mix design using the Personal Consultant Plus expert system development tool. Several useful features for education purposes are discussed. The system is highly interactive and allows the student to ask questions such as WHY an input data is need or HOW a certain parameter or a conclusion is derived. Several graphics images and help messages are incorporated into the system. The system contains answers to several fundamental questions on the mix design process. Programming techniques are also presented. This paper demonstrates that educational software can be easily developed using an expert system development tool.

INTRODUCTION

Computers have been used traditionally in the educational environment as a problem soIving tool. Students have been taught to program computers in various programming languages or to use large application programs. Computers, later, have been used as a teaching tool to enhance the understanding of a certian subject area. A good eductional software should incorporate several features such as the interactive feature, user friendliness, graphical display, and “Glass-box” feature. A considerable amount of time is required to develop such a system using a conventional programming language. A tool could be used to facilitate the development of such software such as the use of LOTUS l-2-3 spreadsheet program[l] as mentioned in a previous work[2].

Recently, the expert system technology has become a new tool in solving problems in various disciplines such as business and engineering. In the past, the development of an expert system was difficult and computer specialists were often needed. The cost to develop a system for educational uses was not justified to many institutions where the educational software development is considered to be a luxury item and of low priority. At present, there are many expert system development tools available commercially[3]. These tools facilitate the development of expert systems. Many of these tools run on low-cost microcomputers. Using expert systems in the educational environment is now justified for both the software development cost and the hardware cost.

An expert system has been developed for teaching concrete mix design to civil and architectural engineering undergraduates. The Personal Consultant Plus (PC Plus) [4] expert system development tool was utilized. The first prototype of this system was reported earlier in an American Concrete Institute publication [5]. Many modifications have been made and many educational features have been added to that prototype such as more explanation screens, more help screens, and etc. Some parts were completely rewritten using different programming approaches.

This paper first describes useful educational features of the Concrete Mix Designer. Pro- gramming techniques are then discussed to show how these educational features were implemented.

EDUCATIONAL FEATURES OF THE CONCRETE MIX DESIGNER

There are many educational features incorporated in the Concrete Mix Designer expert system. This section demonstrates some of these features.

*Present address: Department of Civil Engineering, Christian Brothers College, Memphis, TN 38104-5581, U.S.A.

70 SIRIPONG MALASRI and SANTIAGO M.ALM~ADO

Logic and know/edge base transparency

The student can ask WHY an input data is needed, HOW the value of a parameter is computed, or HOW a conclusion is made. The system responds to WHY and HOW questions by displaying the rule it utilized. Figure 1 shows an input screen where the severe exposure condition is needed. The student may want to know why this information is required in the mix design process. Figure 2 shows the response to the WHY question. Figure 3 shows a conclusion screen. The student may want to know how the system determined the water-cement ratio. The system responds to the HOW question by displaying a rule in the window as shown in Fig. 4. The ability to answer such HOW and WHY questions makes the logic used by the system transparent, The student learns by asking the system questions as he or she would ask an instructor.

The knowledge base of a typical expert system is stored separately from other parts of the system. PC Plus uses IF-THEN rules for knowledge representation which make the knowledge base transparent. Samples of IF-THEN rules are shown in Figs 2 and 4 which can be easily understood by students who do not have any background in expert systems or PC Plus.

HELP facility

PC Plus allows the expert system developer to provide HELP messages for each input parameter. When the system asks for a certain input data, the user simply presses the Fl function key to see help messages. Figure 5 shows a help screen that provides additional information for concrete strength. A help screen could also be replaced by a graphics screen. Graphics help screens are not implemented in the current version of the Concrete Mix Designer since all help messages are relatively short and can be sufficiently described by texts. Using graphics will be discussed in a later section.

Questions and answers

There are several fundamental questions that have been constantly asked by students or those who are new to the concrete technology. Many of these questions were published in an American Concrete Institute publication[6]. Some of these questions and answers were implemented into the system. Figure 6 shows the menu for a list of questions related to the slump determination. Figure 7 shows the answer screen for the first slump question. These questions and answers provide the student with a tutorial on several fundamental concepts in concrete technology.

Using LOTUS 123 graphics for obtaining input data

Water-cement ratio is an important information for the system to determine the proportion of the mix. The system uses a recommended average value suggested in a literature[7]. Depending on types of ingredients used, the value may not follow this recommended average value. Many times the user would like to obtain a more realistic proportion by performing a trial mix in the laboratory.

CONCRETE XIX DESIGNER (Version 2.0)

What is the severe exposure condition of the structure?

Wet continuously and exposed to freezing and thaving. Wet frequently and exposed to freezing and thawing. Exposed to sea water. Exposed to sulfates.

1. Use the arrow keys or first letter o f item to position the cursor. 2. Press RETURN/ENTER to continue.

Fig. 1. An input screen.

Expert system far teaching concrete mix design

CONCRETE HIX DESIGNER (Version 2.0)

71

fhat is the severe exposure condition of the structure?

uet continuously and exposed to freezing and thawing. _1J+..r‘ 1

/

“,.I . ~

Exposure condition is needed to determine maximum water-cement ratio for axpooura condition

RULE010 If I) question for severe exposure is YES, and

2) sire of strxture is All other structures., and 31 1) exposure condition is Wet continuously and exposed to

freezing and thevmq., or 2) exposure condition is Wet frequently and exposed to

freezing and thawing., Then it is definite (100%) that maximum water-cemmt ratio for exposure condition is 0.5.

I l i* End - RETURN/ENTER to continue

2. Press RETURN/ENTER to continue.

Fig. 2. Response to the WHY question.

CONCRETE MIX DESIGNER (Version 2.0)

1 Conclusiono:

Maximum recommended slump inches is as folIous: 3

Hinimum recommended slump inches is as follows: 1

Amount of water in lb/cu.yd. of concrete is as follows: 270

Amount of cement in lb/cu.yd. of concrete is as follows: 566.95652

Rmount of coarse aggregate in lb/cu.yd. of concrete is as follows:

113913

1863.

Amount of sand in lb/cu.yd. of concrete is as folloVs: 1185.55890431074

The Note is es folloua: *** corrections ere needed to compensate for moisture in the aggregates. In practice, aggregates vi11 contain coma measurable amount of moisture. l **

l * End - RETURN/ENTER to continue

Fig. 3. A conclusion screen.

CONCRETE MIX DESIGNER (VOrSiOn 2.0)

elusions:

imum recommended slump inches is as follows: 3

water-cement ratio

Determined to be: 0.46 -.. by using RULE027

If maximum permisible vatar-cement ratio is greater than or equal to 0,

Then 1)

2)

** End

it is definite floor) that maximum pena. waeer-cement r?ItfO, used as goal in the SLUMP frame is maxflaum permisible vater-cement ratio, and it is definite (1002) that water-cement ratio is maximum perm. vat4r-cement ratio, used 1~s goal in the SLUMP frame.

- RETURN/ENTER t0 Continue

Fig. 4. Response to the HOW question.

72 SIRIPOSC MALASRI and SANTIAGO MALDONAW

CONCRETB KIX DESIGNER (version 2.0)

%t is the specified compressive strength psi 7

The knowledge system was developed for normal weight concrete with the strength ranging from 2500 psi to 5000 psi without any admixture. l * End - RETURN/ENTER to continue

1. Enter a positive number. 2. Press P.BTUP.N/ENTER to continue.

Fig. 5. A HELP screen.

A graph of the strength of concrete vs the water-cement ratio is plotted from laboratory results. With this graph, a proper value of water-cement ratio can be read for a desired strength. In the previous system[5], the student has to plot this graph manually to get the water-cement ratio. In the current system, however, the system uses a spreadsheet program where input data from !aboratory can be directly input. The spreadsheet program, then, plots the graph as shown in Fig. 8. The value of water-cement ratio can be read and passed back to the system. This automates the derivation of an input data directly from the laboratory data. The student can also see the effect of the water-cement ratio to the strength of concrete directly from this graph which is a very important concept in the concrete technology.

Using graphics for explanation

Some explanations are better described using pictures than using texts. For each major operation in the Concrete Mix Designer, a graphics screen is displayed. Figure 9 is a graphics screen that explains how a slump is determined in the laboratory.

PROGRAMMING CONSIDERATIONS

This section describes some programming techniques used in implementing educational features of the Concrete Mix Designer.

CONCRETE MIX DESIGNER (Version 2.0)

Please select a SLUMP-frame question:

What iS meant by CONSISTENCY ? What is meant by PLASTIC MIXTURE 7 What is meant by WORKABILITY ? What is the result of having dry and very fluid consistancias 1 Is proper consistency important ? What part does air entrainment play in workability ? Is the slump test a good guide to consistency 1 When is the slump test a useful indication of workability 7 How do we make the slump test ?

1. Use the arrow keys or first letter of item to position the cursor. 2. Press RETURN/ENTER to continue.

Fig. 6. A questions list of the questions/answers.

Expert system for teaching concrete mix design

CONCRETE MIX DESIGNER (Version 2.0)

73

CONSISTENCY is defined as the fluidity of Concrete. It is the ability of freshly aixed concrete to flow. The Usual measure of CONSISTENCY is its slump. l * End - RETD?&/ENTER to continue

Fig. 7. An answer screen of the questions’answers

Water- cement ratio vs strength

4.2 - z 4.4 -

t 3.6 - 'Z $ 3.6 - k 3.4 - E 3.2 -

s 3.0 - I

0.35 0.45 0.55 0.65 0.75

Water -cement ratio

Fig. 8. Spreadsheet graph.

The goal of the SLUMP frame is to determine the slump of the concrete.

1 Slum? test procedure:

Fig. 9. A graphics explanation screen.

SIRPONG MALASRI and SANTIAGO MALDONADO

RULE015 [WC-RULES] ----___

IF: DATA = “available”

THEN: DOS-CALL "C:\LOTUS\123.COM" "123.SET" AND DOS-CALL "GWBASIC.EXE" "A:RENAME" AND READ-FROM-FILE "A:WCRATIO" MAXWCt

Fig. 10. External program interface.

Integrating external programs into the system

PC Plus allows the external program execution External programs can be written in any language as long as they are in the executable form. Concrete Mix Designer executes the LOTUS l-2-3 speadsheet program so that the laboratory data can be plotted and the water-cement ratio can be read as mentioned earlier. Figure 10 shows the rule that performs this task. DOS-CALL is the system function for the external program execution. The external program in this case is the spreadsheet program 1-2-3.COM. The water-cement ratio from the spreadsheet program is then read back to the system using the READ-FROM-FILE system function. Details of interfacing LOTUS l-2-3 spreadsheet program to PC Plus can be found in another work[8]. It should be noted that the rule shown in Fig. 10 is implemented by the developer using the Abbreviated Rule Language (ARL) as opposed to the English translation for the end-user as previously shown in Figs 2 and 4.

Integrating text jile into the system

In the previous version of the system[5], several questions/answers modules were implemented using the external program interfacing technique. These external programs were written in BASIC. Based on a recent experience in developing another expert system for a building code[9], a new better technique has been used. A word processor is used to create ASS11 text files. These text files are read back into the system. Since a text file is treated as a data file to the expert system, it can be later updated, modified, and maintained by the end-user without changing the internal structure of the expert system. Figure 11 shows a sample of a data file named SLUMP1 . RD. This provides an answer to a question related to the slump determination. PC Plus requires the extension RD for all data files. Since PC Plus is a LISP based expert system, all values must be parenthesized. Double quotes differentiate the character type data from the numeric type data. Figure 12 shows a rule that brings up this data file. The READ-FROM-FILE function is used to read the text file into the system which is displayed with the PRINT function.

Integrating graphics into the system

PC Plus allows several ways of incorporating graphics. Graphics can be easily created using a graphics editor, such as TelePaint[lO], PC Palette[ll] etc., or a drafting software, such a AutoCAD [12] etc. A PC Plus utility program is used to capture this picture and store it in a picture file on disk. This graphics screen can be brought up in the system. This picture can be integrated into the expert system as a title screen, an explanation screen, an help screen, an input screen, or a conclusion screen. In the current version of the Concrete Mix Designer, pictures are used only as explanation screens. The Concrete Mix Designer is divided into several parts, each part (or frame) performs a specified task. When a part is entered, an explanation screen is displayed to explain general background related to that particular part. The picture, as shown in Fig. 9, is brought up using a frame property, GPROMPTEVER (graphics prompt). A frame can have several properties in which GPROMPTEVER is a property to display a graphics screen when the frame is activated. Figure 13 shows SLUMP frame properties, where the “SLUMP.GRI” picture

type slumpl.rd

("CONSISTENCY is defined as the fluidity of concrete. It is the ability of freshly mixed concrete to flow. The usual measure of CONSISTENCY is its slump.")

Fig. I I. A sample of an ASCII text file.

Expert system for teaching concrete mix design 75

RULE007 [SLIJMP-RULES: ---s-e_

IF: SLUM?-QVESTION = “yes” AND Q-SLL%P = ‘%%a: is meant by CONSISTS’NCY 7‘

THEN : READ-FROM-FILE “A: SLUMPl” AND PRINT (VALS’E AN.5SLIJMPl)

Fig. 12. ASCII text file interface

CONCRET2 “IX DESIGNER (V.raion 2.0)

rframe propsrttaa:SL”“P TRANSLATION :: Slump determination fruns

co*‘9 :: PIS‘UWP YAY.SL.““P MIHSWYP *“cs‘“up YAXK . . . INITIALDATA :: PASLVMP CPROwT2YER : : “SLUMP”

IDENTIFIER : : “SLUMP-”

IPurp0.e ok- description or the rrame I

file is displayed as a prompt when the frame is entered. Details of how a picture is created and how the utility program is used to capture and store the picture can be found elsewhere[l3].

Creating help messages

Fig. 13. Frame properties.

Help messages are created as a parameter property. A parameter could have several properties similar to frame properties. HELP is a property to display help messages when the student presses the Fl function key. Figure 14 shows the STRENGTH parameter properties where help messages are assigned to the HELP property. The help messages are displayed when requested as shown previously in Fig. 5.

DISCUSSION AND CONCLUSION

Several educational features of the Concrete Mix Designer as well as programming techniques were presented. Using expert system development tools, such as PC Plus, facilitates the devel- opment of an expert system. There are, however, limitations which come with each tool. This is true with the PC Plus package. PC Plus is not designed to handle complex numerical computation

CONCBET2 MIX DESIGNER (Version 2.0)

-Parameter:FCP TRANSLATION ::

PROMPT :: HELP ::

EXPECT :: RANGE ::

TTPE ::

specified compressive strength (psi) Ih.t ia the specified compressive stren;th (-.. Ihe ho.led2e sy,te”, ..s developed f-or norsal . . POSITIVE-NUMBER 2500 5000 SINGLEVALUED

Fig. 14. Parameter properties.

76 SIRIFONG MALASRI and SANTIAGO MALWNADO

which are important in many engineering applications. This limitation, however, can be overcome by using the external program interface as mentioned earlier so that the complex computations can be performed in the external program written in a conventional programming language. The graphics interface mentioned allows only predrawn pictures. These pictures are static. The same external program interface could be used to overcome this limitation such as the use of the spreadsheet graph in the Concrete Mix Designer. This spreadsheet graph is dynamic and changed according to the laboratory data entered by the student. Another limitation of PC Plus is the speed. This limitation will be, however, improved with the advancement of the hardware. PC Plus has several built-in functions for accessing dBASE[13] databases. Records could be added, updated, or retrieved. To use the feature, the user must have an access to the dBASE software. PC Plus does not have its own database management features. It only executes the dBASE software and transfers the data back to the system. This feature, however, is not currently used in the Concrete Mix Designer. Details of the database access can be found elsewhere[ 151. Good education software can be developed in a relatively short time and therefore with a reasonable cost if proper tool and technology are utilized.

REFERENCES

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Engng Educ. 3(l), 55-58 (1987). 3. Harmon P., Maus R. and Morrissey W., Erperr Systems Tools and Applications. Wiley, New York (1988). 4. Texas Instruments. Personal Consultant Plus Version 2.UI (1985). 5. Malasri S. and Maldonado S., Concrete Mix Designer. Stare-of-(he-Art Computer Applications in Concrete Technology

(Edited by Fagundo F.). American Concrete Institute (1988/1989). (In press). 6. McMillan F. R. and Tuthill L. H., Concrete Primer. AC1 Publication SP-I (1987). 7. Portland Cement Association, Design and Control of Concrete Mixtures. 12th edn (1979). 8. Malasri S., PC Plus + LOTUS 123. Microcomputer Knowledge-based Expert Systems in Civil Engineering (Edited by

Adeli H.), pp. 79-87. American Society of Civil Engineers (1988). 9. Malasri S., A prototype expert system for South Florida building code. Proc. 1988 Floridu Sections Meeting of the

American Sociery of Cicil Engineers (1988). IO. LCS/Telegraphics., TelePaint Version 2.2 (1985). Il. IBM., PC Paliette Version 1.00 (1984). 12. AutoDesk Inc., AufoCAD Version 2.52 (1986). 13. Malasri S. and Kengskool K., Graphics interface of an expert system shell. Proc. NCGA’88, National Compufer

Graphics Associafion, Vol. III, pp. 556562 (1988). 14. Ashton-Tate, dBASE III Plus Version I.0 (1986). 15. Malasri S., Data base access using an expert system shell. ICES’88 Post Conference Seminar (Edited by Yamada Y.

and Atluri S. N.), pp. l-10 (1988).