In Civil Engineering (Concrete Structure), If on-site slump test fails, should engineers allow the contractor to continue the concreting works?

the concrete work should not be allowed as failing slum test may indicates that it may effect the durability of concrete which is an important factor.

there are different thoughts on this , but if u considering the durability factor , it should not be allowed.

If Failed to achieve required slump;1-Add  superplasticizer 

http://www.manasanat.com/files/samim/fmng/mahsoolat/TechnologyVaTajhizateBeton/Admixtures/Conplast%SP.pdf

(we are using for Pump-ability & to achieve early days high strength + seconds admixture  mixing in Transit Mixer & your concrete is ready , continue pouring after mixing on the site.

I would rather ask to take the slump test again after remixing again for few minutes to be sure that the mix is homogeneous and the slump result is true, however if it again failed i would unfortunately reject the truck

     If  slump test fails  affect  to  required specification and bearing capacity of construction elements  I will not allow continue works  also depend of how many points fail if it within  rang tolerance  I will continue work second must be considering The density of iron to prevent of Nesting phenomenon of concrete

No allow continue this work 

Change so as to give the required specifications.