Dear Mohammad

Yes, you can use W/C of 0.485 and using superplasticizer to increase the flow value.

Thank

dear Sir Armand Augustin Fondjo ,thank you for your answer.

Mohammad Bany Salman

You can use superplasticizer anytime to improve the flow of mortar/concrete mix. Increasing the W/C for consistency will change a lot of factors (porosity, hydration kinetics, setting time) in your research. The question is not sufficient to guess the reason for low consistency of the mortar mix with W/C of 0.485 and 0.7.

Generally for OPC type 1 the W/C ratio of 0.5 (without any additives or SCM) gives you desired flow. However the flow of mortar decreases significantly with the use of SCM such as smectite clays or calcined clays. Using polycarboxylate based superplasticizer with clays is not a good idea.

Saurabh Khandelwal ,thank you for your replay, actually I have tried to follow the ASTMC109 ,where the w/c ratio is 0.485 and the cement to sand ratio is 1:2.75, the sand used in my case is standard sand, but not graded sand, in w/c of 0.485 the flow value was 24 ,it should be 110+-5 according to ASTM, so I have two choices, first use w/c of 0.7 to get the desired flow value, or use w/c of 0.485 with superplasticizers to get the same flow value

but if you have experience which mix will give higher compressive strength?

Mohammad Bany Salman

from my experience going with low W/C ratio with 110+-5 consistency should give you higher strength. i recommend using superplasticizer (SP) for adjusting the flow but careful with the dosage of SP.

The water / cement ratio must be such that the workability / consistency is adequate for the application of the mortar. In this premise, of course, the properties must meet the requirements established by the literature, aiming at satisfactory performance. However, plasticizer additives can be used, however care must be taken to mitigate adhesion, in view of the possible weakening of the substrate / mortar interface.

João Manoel de Freitas Mota thank you for answer,

yes my sand which was used is standard sand but not graded according to limits of ASTM C778, and my sand used in the mix was air dry not SSD, so in this case it is possible to increase the W/C ratio, isn't it?

Dear Salman, The amount of water must be kept to a minimum, however, adequate for the best condition of workability and consistency for applying the mortar.

João Manoel de Freitas Mota Many thanks for your reply

Dear Salman,

We know that the increase of the water/cement ratio reduces the values of hardened properties and increases the workability. Besides, sand grading seems not to influence the compressive strength. However, it influences the deformations, ductility, and elastic modulus of mortars.

Firstly, I recommend you should reconsider your data. Ordinarily, the appropriate W/C ratio for OPC type 1 gives us desired workability and consistency.

Secondly, you can decrease the w/c with an appropriate dosage of superplasticizer if you do not get the desired flow value. It can be argued that decreasing the w/c with an appropriate dosage of superplasticizer results in an increased number of bonds created by the C–S–H in the percolating particle network of the paste.

Dear Jafarabad, thank you for your good answer

Mohammad Bany Salman dear did you got your answer that what to do with this flow ? I search alot of articles where the flow is 110+5 but in my case i also get the same value (around 15%), i did use ASTM C109.

Dear Waqas Adil ,

I think many parameters affect the flow value, like the condition of sand (air dry or SSD condition) and its gradation. In my case I will use air dry sand, so I will increase W/C ratio to get desired flow value, I hope it works well.

maybe if you used SSD sand with 0.485 W/C it will work!

Mohammad Bany Salman Dear

i used the dry sand. i am following ASTM C 1437. and i am using graded sand as mentioned by ASTM C 109. did you started your experimental work ?

Dear Waqas Adil , I made some pre-tests for this

Fluidity according to ASTM C1437—15 should be use to find the appropriate water-cement ratio for mortar preparation. The fluidity should be 180–220 mm to form a dense mixture and good workability . you should check fluidity according to your parameters

Dear Mohammad Bany Salman,

The smaller the amount of water to obtain adequate workability (consistency, initial adhesion, etc), the better. Among other problems, the more water the mortar contains, the greater the probability of plastic shrinkage cracking. Some factors can help achieve workability (consistency, flow, rheology, etc.), such as: improving the particle composition (this increases the packing of the grains) of the sand and the use of dispersing additives (plasticizers). The latter will add an additional cost to production.

Best regards,

1) If you increase the w/c then you get the desired flow property but it will reduce your strength property and increase the porosity. If that deduction in strength is acceptable then you can increase w/c.

Another problem with higher w/c ratio is bleeding and segregation.

2) usage of admixture can help to improve your flow property without compromising the strength property. Thus it is always recommend to use optimum dosage of SP Instead of increasing w/c.

You can find the answer in this paper

"Evaluation the eect of lime on the plastic and hardened properties of cement mortar and quantied using Vipulanandan model"

Dear all Shivang Jayswal , Ruan Ferreira and Wajahat Sammer Ansari , thank you for your useful answers, I'm really appreciate that

I will add my last updates, I have made mixes with different W/C ratios, ranging from 0.5 to 0.65, with different superplasticizer dosage, except w/c of 0.65, which gave the desired flow value

by looking to the specimen after demolding, I noted that; increasing w/c ratio will reduce the porosity on the surface of cubes, but I will check the compressive strength after curing for the specific period,

again, thank you all

Dear Ahmed Salih Mohammed , thank you for your suggestion

Mohammad Bany Salman

You can test different w/b and perform the flow test. After that you will get different values of w/b and flow, which will make it possible to build a graph (flow x w/b). From this graph, with the equation of the straight line, you can determine the ideal amount of water for the mortar to reach the XXX mm flow, for example.

The water to cement ratio is usually determined by the compressive strength of the cement concrete. Therefore, it is better to use a superplasticizer to increase the flow value without changing the water to cement ratio.