In terms of efficacy, there can be three types of interactions between medications: additive, synergistic, and antagonistic. Additive interaction means the effect of two chemicals is equal to the sum...
condiments are toppings (ie:ketchup, mustard, relish) that one puts on top of your meal, while additives are artificial ingredients and flavour enhancers cooked/baked directly into the food
Additives are added to Cement during manufacturing to get new property for cement whilst admixtures are added to mix during mixing to get new property to the fresh concrete.