Studi pengaruh limbah kertas pada mortar dengan penambahan abu sekam padi dan superplasticizer terhadap kuat tekan, kuat lentur, modulus elastisitas, susut, densitas, dan daya serap air = Study of the effect of waste paper in mortar with addition of fly husk ash and superplasticizer to compressive strength flexural strength elastic modulus shrinkage density and absorption