PHYSICO-MECHANICAL PROPERTIES OF CONCRETE MADE WITH THE MOST USED TYPES OF CEMENTS ADMIXED WITH POLYCARBOXYLATE SUPERPLASTICIZER IN THE CITY OF GOMA, DEMOCRATIC REPUBLIC OF CONGO

International Journal of Engineering and Techniques - Volume 8 Issue 2, April 2022 ISSN: 2395-1303 http://www.ijetjournal.org Page 55 PHYSICO-MECHANICAL PROPERTIES OF CONCRETE MADE WITH THE MOST USED TYPES OF CEMENTS ADMIXED WITH POLYCARBOXYLATE SUPERPLASTICIZER IN THE CITY OF GOMA, DEMOCRATIC REPUBLIC OF CONGO Amadou MOUNDOM 1, 4,*, Trésor MUHATIKANI2, 5 and Olivier BISHIKWABO MAHESHE3,5 1Senior Lecturer in Civil Engineering 2Assistant Lecturer in Civil Engineering 3Master of Engineering Student 4Department of Agricultural Engineering, Faculty of Agronomy and Agricultural Sciences, University of Dschang, Cameroon 5Department of Civil Engineering, Faculty of Sciences and Applied Technologies, Free University of Great Lakes Countries, Goma, Democratic Republic of Congo (*) – Corresponding Author: Email: moundomndi_am[email protected] - ABSTRACT The present work deals with the influence of the dosage of polycarboxylate plasticizer on the physico-mechanical properties of concretes made with the most used types of cements in the city of Goma in the Democratic Republic of Congo. The concretes were designed by Bolomey method using the most used types of cement in the city, namely Hima, Simba and Nyiragongo cements with the most commonly used class 32.5R; the aggregates used are crushed sand 0/4 and crushed gravel 5/20 from the SAFRICAS company based in Goma, the admixture used is polycarboxylate superplasticizer dosed at 0.6% (minimum value for experiment) of the cement mass; tests on the physical properties of the aggregates used and the fresh concrete produced were carried out as well as tests on the mechanical properties of the hardened concrete produced. On adding a minimum amount of polycarboxylate superplasticizer to the most used types of cement in Goma, the workability improved by 77% for Hima cement, 80% for Simba cement and 20% for Nyiragongo cement, which shows that the polycarboxylate plasticizer has more influence in terms of improving the workability of Simba and Hima cements than for Nyiragongo cement; Similarly, the 28 day compressive and tensile strengths of concretes made with above cements improved with the use of the superplasticizer (24% for Hima cement, 32% for Simba cement and 48,1 % for Nyiragongo cement), showing that the polycarboxylate plasticizer improved the Nyiragongo cement concrete more than the Hima and Simba cement concretes. Key words: Admixture, compressive strength, tensile strength, workability, setting, superplasticizer, fresh concrete, hardened concrete. IGENERAL INTRODUCTION I.1 Background In the last decade, the construction sector has experienced a structural development involving the construction of large-scale works and a new technology of construction, which also requires the presence of suitable materials that can meet the requirements of the above-mentioned types of construction. The concrete is among the widely used construction materials and there is need to have it with high strength. As the W (water) / C (cement) ratio is very important for the mix, when W decreases, the strength increases. It is therefore necessary to choose an admixture for the mix that will make the concrete plastic by reducing the water contained in the mixture and thus increasing the concrete's strength in compression and traction. This admixture can be a plasticizer or a superplasticizer. The superplasticizer reduces the water more than the plasticizer and therefore improves the mechanical properties more than the plasticizer. International Journal of Engineering and Techniques - Volume 8 Issue 2, April 2022 ISSN: 2395-1303 http://www.ijetjournal.org Page 56 I.2 Problem statement Concrete made with some natural aggregates as the only components in addition to cement and water often has very poor mechanical properties for use in large structures. Therefore, another non-essential component called admixture is often added in small quantities to the above-mentioned concrete components to improve its performance in terms of strength and workability. I.3 General objective of the research The general objective of this work is to study experimentally the influence of the polycarboxylate superplasticizer on the physico-mechanical properties of the concretes produced with the most used cements in Goma, in order to identify the type of cement that would be the most compatible and favorable with a polycarboxylate superplasticizer admixture to obtain the expected properties. IILITERATURE REVIEW Some previous works relevant to the present work are presented as follows: NA 774 defines a plasticizer as an admixture which, when introduced into a concrete, mortar or grout, has the main function of causing a significant increase in the workability of the mixture and its strength. Guiraud (2018) (2018) worked on the dosage of admixtures function of the weight of cement and the results presented in the table 2.1. Table 2.1: Dosage of admixture function of the weight of the cement Admixtures Dosage in % Plasticizers 0.1 to 1.2 Superplasticizers 0.6 to 2.5 Setting accelerators 1 to 3 Curing accelerators 0.8 to 2 Setting retardants 0.2 to 0.8 Waterproofing 0.5 to 2 Air trainers 0.05 to 3 Air restrictors 0.1 to 2 The compressive strength values of the concretes formulated and manufactured by Cinamula Bashengezi (2018) which varied between 2.6 and 14 MPa. Moundom et al (2016) carried out a physical characterization of black volcanic ash from Baïgom, black pozzolans from Ngouogouo and brown pozzolans from Mfosset in the locality of Foumbot. From this study the fineness modulus varied between 2.09 and 4.21 for the different sands, the sand equivalent varied between 78.9, 96.1%, the absolute densities varied from 2.23 to 2.53 g/cm3 for the pozzolana sands and from 2.06 to 2.37 g/cm3 for the larger particles. Dupain R., Saint-Arroman J.-C. (2009) proposed an approach for the formulation of concrete with light, porous, dry or water-containing aggregates. Moundom et al (2018) carried out the mechanical characterization of lightweight concretes made from granular volcanic materials from the locality of Foumbot with 28-day compressive strength values ranging from 3.87 to 8.26 MPa and proposed their appropriate use in construction. Muhindo (2017) formulated and manufactured the concretes based on Goma aggregates using cements available in Goma and found compressive strengths ranging from 14.5 to 30.4 MPa. Vouffo (2022) worked on black and red pozzolanas from Bafoussam 2 and found compressive strength values ranging from 2.39 and 12.548 MPa. Of all the above-mentioned works, none had experimented with improving the mechanical properties of concretes manufactured in Goma using a superplasticizer such as polycarboxylate. Hence the importance of the present work. III. MATERIALS AND METHODS The laboratory tests were carried out in the Civil Engineering Laboratory of the Faculty of Applied Sciences and Technologies of the Free University of the Great Lakes Countries in Goma, Democratic Republic of Congo (DRC) International Journal of Engineering and Techniques - Volume 8 Issue 2, April 2022 ISSN: 2395-1303 http://www.ijetjournal.org Page 57 III.1 Materials Sand The sand used is 0/4 crushed sand from the SAFRICAS company based in Goma, North Kivu, Democratic Republic of Congo (DRC). Gravel The gravel used is 5/20 crushed gravel from the SAFRICAS company based in Goma, North Kivu, Democratic Republic of Congo (DRC). Cement The cements used are the commonly used cements from all the factories in the city of Goma (DRC) and are Hima, Simba, Nyiragongo and of the more commonly used class 32.5 R. Admixture The admixture used is polycarboxylate superplasticizer at 0.6% (minimum value) of the mass of the cement for experimentation. III.2 Methods III.2.1. Tests to determine the physical properties of the aggregates and binders used III.2.1.1. Dry particle size analysis of 0/4 sand and 5/20 gravel. The particle size analysis was carried out by dry method using an electric sieve shaker in accordance with the requirements of standards EN 933-2 (May 1996) and NF P 18-560. At the end of this particle size analysis test, the fineness modulus (FM) was determined on the one hand, and the coefficient of uniformity (Cu) and that of curvature (Cz) on the other. The fineness modulus (FM) is determined according to the XP P 18-540 standard by relation 1: 𝐅𝐌 = ∑𝐑𝐞𝐟𝐮𝐬 (𝟓;𝟐,𝟓;𝟏,𝟐𝟓;𝟎,𝟔𝟑;𝟎,𝟑𝟏𝟓;𝟎,𝟎𝟖) 𝟏𝟎𝟎 (1) The uniformity coefficient (Cu) and that of curvature (Cz) are defined by relations 2 and 3. Cu = d60 d10 (2) 𝐶𝑧 = 𝑑30 2 𝑑10𝑥𝑑60 (3) Where dy is the diameter of the sieve corresponding to y% of cumulative passings. III.2.1.2. Sand equivalent test The sand equivalent (SE) test was carried out in accordance with the requirements of standard NF P 18598. This test allows us to check the degree of cleanliness of a sand, which is equivalent to highlighting traces of clay, as the presence of clay in the concrete greatly reduces its strengths during hardening, as the clay absorbs part of the water in the concrete to form the sludge that hinders the adhesion of the cement with the aggregates. The sand equivalent (SE) is the average between visually sand equivalent (SEv) and the piston sand equivalent (SEp). The values of (SE), (SEv) and (SEp) are given by the relations 4, 5 and 6: 𝐒𝐄 =𝐒𝐄𝐕+𝐒𝐄𝐏 𝟐 (4) International Journal of Engineering and Techniques - Volume 8 Issue 2, April 2022 ISSN: 2395-1303 http://www.ijetjournal.org Page 58 𝑺𝑬𝑽=𝑯𝟐 𝑯𝟏 x 100 (5) 𝑺𝑬𝒑=𝑯𝟐 𝑯𝟏 x 100 (6) Where Height of clean sand plus fines is H1 and the height of clean sand only is H2, measured visually for (SEv) or measured with the piston for (SEp). III.2.1.3. Absolute density test The absolute density was determined according to the standards NF P 18-554 for gravel and NF P 18-555 for sand. The method used was the graduated cylinder test method. It consisted in measuring the mass per unit volume of solid material without any void between the grains by pouring a known mass of aggregate into a quantity of water. The difference in volume relative to the mass of the material gave the absolute density. The absolute density is given by the relation 7 : 𝛒𝐚𝐛𝐬 = 𝐌 𝐕𝟐−𝐕𝟏(𝐠/𝐜𝐦𝟑) (7) Where: - M is the dry mass of the material and, - V1 and V2 are the readings on the test piece before and after the placement of the aggregate in the test piece. III.2.1.4. Setting and normal consistency tests on cements ➢ Cement setting Three types of cement were used: HIMA, SIMBA and NYIRAGONGO, all of which comply with NF P 15-301 and ENV 197-1. The measurement of the setting time was carried out in accordance with the requirements of standard EN 196-3. The presence of setting regulators in the mass of hydraulic binders allows them, after mixing, to set after a few hours. It is therefore necessary to know the setting time of hydraulic binders in order to determine the time available for in situ application of the mortars and concretes from which they are made. The tests are carried out with the help of the Vicat needle which gives two practical reference points: the beginning of setting and the end of setting. ➢ Normal cement consistency Three types of cement were also used: HIMA, SIMBA and NYIRAGONGO, all of which comply with standards F P 15-301 and ENV 197-1. The consistency of the paste characterises its greater or lesser fluidity. Two standardized tests allow this consistency to be assessed, namely the consistency test carried out with the Vicat apparatus in accordance with standard EN 196-3 and the cone flow test, in accordance with standard NF P 18-358. The consistency of our different types of cement was determined using the Vicat test according to EN 196-3. III.2.2. Mix design of the concrete The BOLOMEY method (Dreux and Festa) is used for the design of the different concrete mixes with the design parameters given in Table 3.1. Table 3.1: Concrete design parameters for the Bolomey method Materials Absolute density Bulk density Cement 3.10 1,00 Crushed sand 0/4 2,50 1,57 Crushed gravel 5/20 2,63 1,232 The cement dosage used is 400 kg/m3 for a slump of 14 cm III.2.3 Physical test on fresh concrete - Abrams Cone Settlement Test The workability of the concrete was assessed using the Abrams cone, in accordance with the requirements of standard NF P 18-451. The C/W ratio is kept constant for the design with each type of cement. International Journal of Engineering and Techniques - Volume 8 Issue 2, April 2022 ISSN: 2395-1303 http://www.ijetjournal.org Page 59 The test consisted of introducing fresh concrete into a truncated cone mould (D = 20, d = 10, H = 30 cm) in three layers, where each layer was pitted 25 times with a 16 mm diameter rod, then the mould was slowly removed and the slump measurement was taken. III.2.4 Mechanical tests on hardened concrete III.2.4.1. Compression test This test allows us to determine the compressive strength of a concrete specimen, using a machine called a concrete press. This determination of the simple compressive strength of concrete after days of immersion was carried out in accordance with standard NF EN 12390-3. The compressive strength (fc) in MPa is the ratio between the compressive force F in N that causes rupture of specimen and the area of the base surface of the specimen (S) in mm2, given by the relation 8: 𝒇𝒄=𝑭 𝑺 (8) III.2.4.2. Tensile test The values for the tensile strength at d days are calculated using the expression 9: 𝑓𝑡= 0,6 + 0.06𝑓 𝑐. (9) where fc and ft are in MPa. - IVRESULTS AND DISCUSSION IV.1 Physical properties of the aggregates and binders used IV.1.1. Granulometric composition ➢ Sand 0/4 studied The granulometric composition of the sand studied is presented in Table 4.1.a and Figure 4.1.a. Table 4.1.a: Size composition of the sand studied Sieve No. Opening in mm Cumulative retained Cumulative Passing ASTM AFNOR ASTM AFNOR g % % 3/16'' 38 5 5 10 0,512820 99,487179 5 37 4 4 55 2,8205128 97,179487 6 36 3.15 3.15 225 11,538461 88,461538 8 35 2.5 2.5 450 23,076923 76,923076 10 34 2 2 650 33,33333 66,666666 12 33 1.68 1.6 820 42,051282 57,948717 16 32 1.25 1.25 960 49,23076 50,7692 0.63 1200 61.538 38.461 40 27 0.4 0.4 1430 73,333333 26,666666 50 26 0.315 0.315 1490 76,41025 23,589743 100 23 0.16 0.16 1755 90 10 200 20 0.08 0.08 1890 96,923076 3,0769230 International Journal of Engineering and Techniques - Volume 8 Issue 2, April 2022 ISSN: 2395-1303 http://www.ijetjournal.org Page 60 Figure 4.1.a: Particle size distribution curve of crushed sand 0/4 studied As a result of the sieve analysis of the sand, the coefficient of uniformity and the coefficient of curvature as well as the fineness modulus are presented in Table 4.1.b. Table 4.1.b: Coefficient of uniformity, coefficient of curvature and fineness modulus of the 0/4 sand studied Material d10 d30 d60 Coefficient of uniformity (Cu) Coefficient of curvature (Cz) Fineness modulus (FM) Sand 0/4 0,16 0,47 1,69 10,59 0,80 2,7 The fineness modulus values in Table 4.1.b show that the grain size of our sand is acceptable for making good quality concrete, especially since it is between 2.2 and 2.8. This fineness modulus value of 2.7 similar to 2.76 determined by Muhindo (2017), is higher than the value of 2.09 determined by Moundom et al (2016) on the black volcanic ash sands of Baigom by Foumbot, the 2.4 determined by Cinamula Bashengezi (2018) on the 0/4 sand of Safricas in Goma in DRC, but well below the values of 4.21 for black pozzolan sand and 4.07 for brown pozzolana sand from Mfosset determined by Moundom et al (2016) and also well below the values of 5.43 for black pozzolanas and 4.73 for red pozzolanas from Bafoussam 2 in Cameroon determined by Vouffo (2022). The values of coefficient of uniformity (Cu) and coefficient of curvature (Cz) are respectively 10.59 and 0,8. Since one of the conditions Cu > 6 and Cz between 1 and 3 is not satisfied, the sand grading is poor (Robitaille and Tremblay, 1997). These values are similar to the values determined by Muhindo (2017) but different from the values found by Moundom et al (2016) and Vouffo (2022). ➢ Gravel 5/20 studied The granulometric composition of the gravel studied is presented in Table 4.1.c and Figure 4.1.b. Table 4.1.c: Size composition of the 5/20 gravel studied Sieve No. Opening in mm Cumulative retained Cumulative Passing ASTM AFNOR ASTM AFNOR g % % 3/4 '' 44 20 20 0 100 2/3'' 43 16 16 65 2,1739130 97,826087 ½'' 42 12.5 12.5 505 16,889632 83,1103679 3/8'' 41 10 10 1195 39,9665552 60,0334448 1/3'' 40 8 8 1694 56,655518 43,3444816 ¼'' 39 6.3 6.3 2445 81,772575 18,227424 3/16'' 38 5 5 2770 92,642140 7,35785953 5 37 4 4 2940 98,3277592 1,6722408 6 36 3.15 3.15 2985 99,8327759 0,16722408 8 35 2.5 2.5 2990 100 0 10 34 2 2 2990 0 20 40 60 80 100 120 0.0001 0.001 Percentage passing Particle size (mm) x 10000 Particle size distribution curve of crushed sand 0/4 International Journal of Engineering and Techniques - Volume 8 Issue 2, April 2022 ISSN: 2395-1303 http://www.ijetjournal.org Page 61 Figure 4.1.b: Particle size distribution curve of crushed gravel 5/20 studied As a result of the gravel size analysis, the coefficient of uniformity and coefficient of curvature are presented in Table 4.1.d. Table 4.1.d: Coefficient of uniformity and coefficient of curvature of the gravel 5/ 20 studied Material d10 d30 d60 Coefficient of uniformity (Cu) Coefficient of curvature (Cz) Gravel 5 /20 5,32 7,1 10,00 1,88 0,95 According to Tables 4.1.c, 4.1.d and Figure 4.1.b, the values of the Coefficient of uniformity (Cu) and the Coefficient of curvature (Cz) of the gravel are 1.88 and 0.95 respectively. Since one of the conditions Cu > 4 and Cz between 1 and 3 is not satisfied, the gravel grading is poorly graded (Robitaille and Tremblay, 1997). These values are similar to the values determined by Muhindo (2017) but different from the values found by Moundom et al (2016) and Vouffo (2022). IV.2 Sand equivalent The values of the sand equivalent studied are presented in Table 4.2. Table 4.2: Sand equivalent values of the sand studied Sand SEV (%) SEP (%) SE (%) SE (Mean) Sample 1 83,38 87,6 85,49 85,72 Sample 2 85,6 86,33 85,965 According to Table 4.2, the sand equivalent value is 85.72 This value is higher than 80 and according to the Dreux classification scale (1981), the sand is very clean. The almost total absence of fine may lead to a plasticity defect in the concrete, which must be corrected by increasing the cement dosage. This value of 85.72 is different from 90.1 and 92.5 determined respectively by Muhindo (2017) and Cinamula Bashengezi (2018) on a sand from the same locality, and also different from the values 91.7 and 94.8 determined by Vouffo (2022) respectively on black pozzolanas and red pozzolanas of Bafoussam 2. The same value is different from the values 78.9, 96.1 and 95.5 determined by Moundom et al (2016) for Baigom volcanic ash sand, Ngouogouo black pozzolana sand and Mfosset brown pozzolan sand by Foumbot respectively. IV.3 Absolute density The absolute density values of the studied aggregates are presented in Table 4.3. Table 4.3: Absolute density of 0/4 sand and 5/20 gravel from SAFRICAS Aggregates Mass (g) V1 (ml) V2 (ml) ρabs (g/ml or g/cm3) 0/4 sand from SAFRICAS 500 500 690 2,5 5/20 gravel from SAFRICAS 500 500 690 2,63 -20 0 20 40 60 80 100 120 110 100 Percentage passing Particle size (mm) Particle size distribution curve of crushed gravel 5/20 International Journal of Engineering and Techniques - Volume 8 Issue 2, April 2022 ISSN: 2395-1303 http://www.ijetjournal.org Page 62 The value of absolute density found in Table 4.3 meets the condition of the BOLOMEY method that the absolute density of aggregates should be between 2.5 and 2.7 g/cm3. These values are similar to the values of 2.61 g/cm3 and 2.59 g/cm3 determined by Muhindo (2017) and 2.6 g/cm3 and 2.59 g/cm3 determined by Cinamula Bashengezi (2018) for sand and gravel from Safricas respectively. These values are different from those determined by Vouffo (2022) which vary between 2.68 g/cm3 and 2.74 g/cm3, and globally those determined by Moundom et al (2016) which vary between 2.23 and 2.53 g/cm3 for pozzolana sands and between 2.06 and 2.37 g/cm3 for larger particles. IV.4. Setting and normal consistency on cements IV.4.1. Setting of the cement The setting values of HIMA, SIMBA and NYIRAGONGO cements present in Goma for a quantity of mixing water obtained during the consistency test and a plasticizer dosage of 0.6% are presented in Table 4.4. Table 4.4: Setting values of different cements mostly used in Goma Type of cement Polycarboxylate free With 0.6% polycarboxylate Beginning of setting End of setting Beginning of setting End of setting Hima 4 hr 33 min 6 hr 20 min 7 hr 15 min 9 hr 20 min Simba 4 hr 20 min 6 hr 10 min 7 hr 25 min 9 hr 40 min Nyiragongo 4 hr 20 min 6 hr 10 min 5 hr 40 min 7 h min35 The results in Table 4.4 show that the polycarboxylate superplasticizer has an influence on the beginning of setting time of different cements used in Goma, but also on the setting time of the cements. For Hima cement without polycarboxylate plasticizer, we have a beginning of setting time of 4 h 33 min for an end setting time of 6 h 20 min, and when the plasticizer is used, we see that the beginning of setting time becomes 7 h 15 min for an end setting time of 9 h 20 min. Thus, we can say that the polycarboxylate plasticizer has a great influence on the beginning of setting time for Hima cement, this increase is 2 h 42 min and is explained by the fact that the plasticizer increases the fluidity of the paste, while the setting time also increases by 18 min. For Simba cement without polycarboxylate plasticizer, we have a beginning of setting time of 4 h 20 min for an end setting time of 6 h 10 min, and when the plasticizer is used, we find that the beginning of setting time becomes 7 h 25 min for an end setting time of 9 h 40 min. Thus, we can say that the polycarboxylate plasticizer also has an influence on the beginning of setting time for Simba cement, this increase is of 3 h 05 min and is also explained by the fact that the plasticizer increases the fluidity of the paste while the setting time also increases by 25 min. For Nyiragongo cement without polycarboxylate plasticizer, we have a beginning of setting time of 4 h 20 min for an end setting time of 6 h 10 min, and when a plasticizer is used, we see that the beginning of setting time becomes 5 h 40 min for an end setting time of 7 h 35 min. Thus, we can say that the polycarboxylate plasticizer also has an influence on the beginning of setting time for Nyiragongo cement, this increase is of 1h 20 min and is explained by the fact that the plasticizer increases the fluidity of the paste while the setting time also increases by 5 min. From the results obtained above, we can see that in the presence of the 0.6% polycarboxylate plasticizer, Nyiragongo cement requires less beginning time to set and less time to set than the other two types of cement. These results are similar to those determined by Muhindo (2017) and Cinamula Bashengezi (2018). IV.4.2. Normal consistency of cement The results of the consistency of cement mostly used in Goma with and without polycarboxylate plasticizer are presented in Table 4.5. Table 4.5: Normal consistency values of different cements mostly used in Goma Types of cements Quantity of water in %. Without Polycarboxylate With 0.6% polycarboxylate Hima 35 27 Simba 31 28,5 Nyiragongo 27,3 27 International Journal of Engineering and Techniques - Volume 8 Issue 2, April 2022 ISSN: 2395-1303 http://www.ijetjournal.org Page 63 From the results of Table 4.5, polycarboxylate superplasticizer has an influence on the consistency of different cements mostly used in Goma. Thus, for a polycarboxylate dosage of 0.6 %, we have a reduction in the quantity of mixing water of 8 % for Hima cement, 2.5 % for Simba cement and 0.3 % for Nyiragongo cement. We can say that the action of the polycarboxylate plasticizer on the consistency of the cement is more important for Hima cement than for Simba and Nyiragongo cements, so Hima cement requires less mixing water than the other two cements when polycarboxylate plasticizer is added to its concrete. IV.5. Concrete mix design The concrete mix design determined by BOLOMEY method and used in this work is presented in Table 4.6. Table 4.6: Concrete mix Components of concrete Quantity for 1 m3 of concrete by mass Cement 400 kg Sand 0/4 1094.76 kg Gravel 5/20 378 kg Water 224.78 kg Admixture (Polycarboxylate Superplasticizer) 0.6% of cement mass Total 2097.4 kg+0.6% cement mass for admixture Table 4.6 shows that the concrete mix by Bolomey method gives for one m3 of concrete, 400 kg of cement, 1094.76 kg of sand 0/4, 378 kg of gravel 5/20 and 224.78 kg of water. This is in accordance with the current concrete mix ratio of one sand to two gravels and a mass ratio (W/C) of 0.56. These dosages are similar to those determined by Muhindo (2017) and Cinamula Bashengezi (2018). - IV.6 Physical properties of fresh concrete ➢ Subsidence at the Abrams cone The slump cone values of fresh concrete are presented in Table 4.7. Table 4.7: Slump cone values of fresh concrete Types of cement Settlement in cm Without Plasticizer With 0.6% plasticizer Hima 4.5 8 Simba 5 9 Nyiragongo 5 6 Based on the results of Table 4.7, polycarboxylate has an influence on the workability of the different cementbased concretes produced in Goma, without changing the C/W ratio. We observe an increase of 77% in slump cone values for Hima cement, 80% for Simba cement and finally 20% for Nyiragongo cement. Hence the polycarboxylate has little influence on workability and is less suitable for Nyiragongo cement than for the other two types of cements. IV.7 Mechanical properties of hardened concrete produced without polycarboxylate plasticizer - IV.7.1. Compressive strength of hardened concrete without plasticizer The results after compression of concrete specimens at different ages and cement types studied and without plasticizer are presented in Table 4.8 and Figure 4.2. Table 4.8: Compressive strength based on the types of cements studied and without plasticizer Concrete Compressive strength (without plasticizer) (MPa) 7 days 14 days 28 days With Hima cement 10,54 11,19 13,89 With Simba cement 11,35 12,06 16,25 With Nyiragongo cement 9,86 10,47 13